Instead, a forearm injury sidetracked him in May and again in July. Now his future is even more uncertain.
Taillon will miss the 2020 season after undergoing Tommy John surgery on his right elbow for a second time.
The team said Wednesday that Taillon had the operation a day earlier in New York. The club initially hoped Taillon would need surgery on only his right flexor tendon, but during the operation, Dr. David Altchek determined that Taillon also needed surgery to repair the ulnar collateral ligament in the elbow.
"I haven't had a chance to talk to him personally yet. I reached out to him yesterday. I received the news yesterday, so, yeah, it wasn't the result or the finding that we were looking for or hoping for," Pirates manager Clint Hurdle said before Wednesday's game at the Los Angeles Angels.
"However, now we'll deal with the reality of what it is and do everything we can to support him again, encourage him. And I'm sure there will be a point and a time and place where he will figure out what his next steps are," he said.
Taillon, 27, had Tommy John surgery in April 2014 while still in the minors. He missed the 2015 season with a sports hernia before returning in 2016 and making his major league debut later that year.
Taillon went 2-3 with a 4.10 ERA in seven starts for Pittsburgh this season. He felt pain in his right forearm following his last start against Texas on May 1, and the team shut him down for nearly two months.
Taillon returned to throwing in late June before having pain again in late July.
"Although Jameson is disappointed in this outcome, he is most disappointed that he won't be able to compete with his teammates next year, compete for his fans, compete for the city of Pittsburgh," Pirates director of sports medicine Todd Tomczyk said. "Fortunately, Jameson has been through some setbacks before throughout his career, and he is bound and determined to make this another comeback."
As far as research on players who twice have had Tommy Jon surgery, "there is not a lot, but there is enough," Tomczyk said.
"I think with Jameson, it's a work in progress. I think the early initial phases of the rehab are just beginning. And how this all plays out for him, I know that he's confident that he will pitch again in the major leagues."