For weeks, Phillies reliever David Robertson has known that he wouldn’t pitch again this season.

Now, he's faced with the possibility that he might never pitch again for the Phillies at all.

Robertson underwent a reconstruction of the ulnar collateral ligament in his right elbow -- commonly called Tommy John surgery -- on Thursday, Phillies manager Gabe Kapler said Saturday. Because the procedure also entailed the repair of Robertson’s flexor tendon, the veteran reliever isn’t expected to be able to pitch in games for 14-16 months, which would put him out for all of next season and bring him to the end of a two-year, $23 million contract.

"Obviously he's super disappointed and wants to be contributing to what we're doing right now," said Kapler, who has spoken with Robertson by phone since the procedure. "I think he's apologetic because it's hard to have an injury like this occur and feel like all you want to do is contribute and not be able to do it. It's a rough time for him."

Robertson turned to Twitter and described his predicament as “heartbreaking,” while pledging to return before the end of next season.

The Phillies signed Robertson in part because he had been among the most durable relievers in baseball over the last decade. From 2010-18, he made 584 appearances, fourth in the majors behind Tyler Clippard (649), Brad Ziegler (623) and Fernando Rodney (588).

But Robertson appeared in only seven games for the Phillies and posted a 5.40 earned-run average before being sidelined with a strained flexor tendon. He attempted to come back from the injury but endured a slower-than-expected progression and several setbacks.

Late last month, Robertson announced he wouldn't pitch again this season and feared that he would need Tommy John surgery. After a consultation with prominent surgeon Dr. James Andrews, he went ahead with the procedure, which was performed by Andrews.

Robertson isn’t the only veteran Phillies reliever who has been healthy for most of his career before having injury troubles with the Phillies. Tommy Hunter and Pat Neshek combined to make only 25 appearances this season after signing two-year contracts worth $18 million and $16.25 million, respectively, before last season.