The New York Mets optioned struggling right-hander Zack Wheeler to Triple-A Las Vegas on Saturday.

"They just pulled me in, like everybody else, and told me, 'You're going to Triple-A,'" Wheeler told reporters Saturday. "You take it kind of hard, because you're so used to being up here. It gives me a chance to go down there and just fine-tune some things and work on some things I need to work on to get back up here and be consistent.

"I really haven't proven myself this spring, so I sort of saw it coming, but I was hoping that it wouldn't. ... I really haven't done that much to help my cause."

With Jason Vargas possibly starting the season on the disabled list with a hand injury, Wheeler was contending for the No. 5 spot in the rotation, which likely will go to Seth Lugo, as well as a bullpen spot.

Vargas, who suffered a nondisplaced fracture of the hamate bone in his right hand last week, told reporters Saturday that he went to the emergency room Friday after a bad reaction to prescribed painkillers. His bullpen session was pushed back a day.

Wheeler threw 58 pitches in his last spring appearance Thursday, allowing five runs (three earned) on seven hits with three strikeouts. Lugo, meanwhile, pitched four scoreless innings.

In five spring outings, Wheeler has given up nine earned runs in 10 innings, striking out 14.

He was 3-7 with a 5.21 ERA in 17 starts for the Mets in 2017, with 81 strikeouts and 40 walks.

"It was very difficult," manager Mickey Callaway said in Jupiter, Florida, where the Mets lost to the St. Louis Cardinals 8-7 in an exhibition game. "I think that Wheeler's got a lot to offer the team. I think that we all feel -- I think even Wheeler feels -- that there's some things to work on. In my mind he needs to get out there and pitch consistently and I think being in the Triple-A rotation will allow him to do that."