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Dr. Nicholas Greiner serves as a primary care & internal medicine physician with the St. Louis Cardinals medical staff.

Dr. Greiner earned his medical degree from Kirksville College of Osteopathic Medicine and completed a Family Medicine residency at the University of Missouri-Columbia. He completed a Primary Care Sports Medicine fellowship at Saint Louis University. He has a certificate of added qualification in Sports Medicine.

Dr. Greiner is in his eighth year of practice, and beginning his third year with Mercy Sports Medicine. He has served as a team physician for the University of Missouri-St. Louis for the past six years and was the head team physician for the St. Louis F.C. professional soccer team for the last five years. He has also provided game coverage for numerous NCAA and other local sporting events.

Dr. Greiner lives in the city of St. Louis with his wife Meaghan.

Dr. Thomas Horn is a board-certified psychiatrist and fellow of the American Psychiatric Association. He has more than a decade of experience delivering compassionate,
evidence-based, integrative mental health care. Currently serving as Mercy’s chief physician executive of behavioral health, he’s leading the integration of behavioral health and psychiatry into primary care and emergency department workflows and overseeing mental health partnerships across Mercy’s East region.

Dr. Horn joined Mercy in 2016. Previous leadership roles include regional chair of medical specialties and neuroscience service line chair. He’s also a psychiatric consultant for the St. Louis Cardinals and a co-founder of the American Board of Sports and Performance Psychiatry.

Dr. Horn earned his medical degree from the University of North Texas Health Science Center in Fort Worth, where he also finished additional training in health management and policy. Dr. Horn completed his psychiatry residency and served as chief resident at the University of Oklahoma in Tulsa. His clinical practice spans outpatient psychiatry, collaborative care and integrated behavioral health models, with prior service in both community mental health and inpatient settings.

Dr. Horn is also a dedicated advocate for physician wellness and public mental health education. Outside of his clinical and leadership roles, he’s actively involved in service and mentorship through organizations like the Boy Scouts of America and as a coach for his children’s youth sports.

Dr. Brian Mahaffey has been a member of the St. Louis Cardinals medical staff as a team physician for 22 years. He now serves the Cardinals organization as the director of sports medicine. Prior to coming to St. Louis in 2013, he served as team physician with the Springfield Cardinals (Double-A affiliate) for nine years in Springfield. 

Dr. Mahaffey is medical director of Mercy Sports Medicine and is with Mercy Clinic Sports Medicine. He helped develop a regionally known sports medicine program in Springfield, from the foundation laid prior to his arrival. He served as head physician for the Missouri State University athletics program for 16 years. He served as head team physician for Lindenwood University as Mercy established their partnership in 2023, until 2025, and still serves as a team physician. He was the medical director for the Missouri State University Athletic Training and Sports Medicine academic program and currently serves in the same role for the Lindenwood University academic program.

Dr. Mahaffey's interest in baseball is lifelong. He attended Missouri State University, where he played baseball while earning a bachelor’s degree in biology. He was named the Conference Co-Player of the Year in 1988 and graduated with 10 annual and career records. He was a three-time Academic All-American. He has been inducted into the MSU Athletic Hall of Fame and into the first class of MSU's Academic Hall of Fame for Athletics. He was also inducted into the Missouri Sports Hall of Fame and the Springfield Area Sports Hall of Fame. Earlier this year, as director, he was proud of the induction of the Mercy Sports Medicine Athletic Training Program into the Missouri Sports Hall of Fame. This summer, he will be inducted into the Missouri State Sports Medicine Hall of Fame.

Dr. Mahaffey graduated from the University of Missouri - Columbia School of Medicine in 1993, where he earned a Master of Science in Public Health, completed a residency in family and community medicine, completed a fellowship in Sports Medicine and Academic Medicine and earned a Primary Care Sports Medicine Certificate of Qualifications. 

Originally from Springfield, Dr. Mahaffey and his wife, Sandra, now live in St. Charles. They are proud parents of two daughters: Lauren and Samantha. 

Dr. Shalen Kouk joined the St. Louis Cardinals medical staff in 2023 and serves as Head Team Physician.

Dr. Kouk earned his undergraduate degree from Cornell University in Ithaca, New York, and his medical degree at Case Western Reserve University Medical School in Cleveland, Ohio. He then completed his Orthopedic Surgery residency training at NYU Langone Medical Center in New York City and his Sports Medicine fellowship in Birmingham, Alabama at the American Sports Medicine Institute and renowned Andrews Sports Medicine Center. 

Prior to joining the Mercy Clinic, Dr. Kouk cared for athletes from high school, NCAA Division I collegiate and professional sports. He has written several publications and book chapters focusing on treatments for orthopedic injuries as well as UCL (ulnar collateral ligament) repair, also known as Tommy John surgery, in baseball players.

Dr. Kouk lives in St. Louis with his wife, who is a urologic oncologist.

Dr. Steffes is in his first year with the St. Louis Cardinals medical staff as a Team Orthopaedist. Prior to joining the team, he served as an assistant team physician for both the Los Angeles Dodgers and Angels baseball clubs.

Dr. Steffes is with Mercy Clinic Orthopaedic Surgery. He received his medical degree from Wayne State University and completed an orthopedic residency at the University of Illinois. Dr. Steffes then completed an orthopedic sports medicine fellowship at the Kerlan-Jobe Orthopaedic Clinic where he provided care for the Los Angeles Rams, Galaxy, Sparks, Dodgers, Angels, Anaheim Ducks, PGA Tour. At the collegiate level, he has been a part of the medical team for the University of Southern California, Loyola Marymount and Pepperdine Universities.

Dr. Steffes lives in St. Louis with his wife, Marcella, and their family.

Dr. Christian Verry serves as a primary care & internal medicine physician with the St. Louis Cardinals medical staff.

Dr. Verry is core faculty with Mercy family medicine residency, and an adjunct assistant professor at Saint Louis University School of Medicine, Department of Family and Community Medicine. He also serves as medical director for Hotel California by the Sea, a local addiction treatment center.

Dr. Verry earned his medical degree from the University of Missouri-Columbia and completed a family medicine residency at Swedish Family Medicine in Littleton, CO. He also completed a sports medicine fellowship at the University of Oklahoma at Tulsa.  He holds a certificate of added qualifications in sports medicine.

During his career, Dr. Verry has cared for athletes in a variety of settings. He has served as head team physician for the University of Vermont, as team physician for Saint Louis University and as part of the medical team for the St Louis Ambush. He has also provided coverage for numerous semi-professional and NCAA events.

Dr. Verry lives in the St Louis area with his wife, Teresa, and their three young boys.