PORT ST. LUCIE, Fla. -- Before a torn ulnar collateral ligament wiped out Zack Wheeler's season, the Mets worried about a different issue in his troublesome right elbow: a torn tendon.

The tendon tear, a source told Newsday, is what prompted Wheeler to undergo platelet-rich plasma therapy twice this offseason. Doctors hoped the treatment would speed up healing and allow Wheeler to keep pitching. They thought that the rest and the PRP would allow it to calm down," the source said. "And it didn't . . . For whatever reason, it didn't help, it didn't take."

Wheeler, 24, had been cleared to keep pitching last season despite chronic pain caused by what the team has been calling inflammation of the tendon, or tendinitis. According to a source, it turns out that the tendon was actually "a little bit torn."

Wheeler's elbow ligament, meanwhile, showed no signs of a tear until Saturday. That's when lingering pain prompted an MRI exam on Saturday.

On Wednesday, Wheeler was examined by team doctor David Altchek in New York. According to the source, Altchek confirmed a "pretty substantial" tear of Wheeler's UCL, which had been expected.