Pittsburgh Pirates starting pitcher Jameson Taillon underwent surgery for suspected testicular cancer on Monday, the team announced.
The 25-year-old right-hander was originally placed on the 10-day disabled list Saturday due to groin discomfort.
An abnormality was discovered, and Taillon and his doctors decided surgery was the best course of action.
"Jameson has again proven to us what a strong person he is by the way in which he has reacted to this development," Pirates general manager Neal Huntington said in a statement.
"We are appreciative of Dr. [John C.] Lyne and the staff at Allegheny General Hospital for their invaluable expertise and efforts in caring for Jameson.
"We have told Jameson that our only priority is his health and well-being. His team-mates, our coaches, baseball staff and entire organisation will support him in his recovery in every possible way and we will keep him in our thoughts and prayers."
Taillon would be eligible to return from the disabled list May 14, but that likely will change based on his recovery and treatment plan.
Huntington said a timeline for Taillon's recovery at this point is unclear.
It is the latest setback for Taillon, who as the Pirates' top prospect in 2014 underwent Tommy John surgery and had sports hernia surgery in 2015.
He was also struck in the head by a line drive as a rookie last season.
Taillon, a rising star in his first full MLB season with the Pirates, has a 2-1 record with a 3.31 ERA and 30 strikeouts in 35.1 innings pitched.