DENVER -- As the only starter left standing from the Mets' Opening Day rotation, Mike Pelfrey's struggles in his past two starts have forced some concern on the club's part about the rotation's prognosis for the 2010 season.

Johan Santana and Oliver Perez each underwent surgery on Tuesday for the removal of bone chips in Santana's left elbow and the removal of scar tissue from Perez's left knee. John Maine is working his way back after nearly three months on the disabled list with right shoulder weakness, and Livan Hernandez was released in August.

Mets starters Jonathon Niese (torn hamstring tendon) and Fernando Nieve (muscle tear in thigh) are also on the DL.

"From all indications, I don't think there'd be any question about Johan [being ready for Spring Training]," manager Jerry Manuel said Wednesday before the middle game of a three-day set with the Rockies. "But if you have surgery, you have surgery. Jonathon Niese was not an arm injury. Nieve was not an arm injury. Oliver Perez was not an arm injury. There is somewhat of a cloud, but it's not as cloudy [as it sounds]. It's partly cloudy."

After going 13-11 with a 3.72 ERA in his first full season in the Majors in 2008, Pelfrey generated high hopes. The Mets have not lost their optimism about the 25-year old right-hander, despite Pelfrey's no-holds-barred assessment of his pitching in Tuesday's 8-3 loss to the Rockies, when he gave up seven runs (six earned) on six hits and five walks in four innings.

"I got what I deserved," Pelfrey said. "I went out there and I was terrible and I got the loss. I feel more bad for my teammates who had to stay out and had to play behind that. I was terrible and that [stinks] for them. I was absolutely awful."

The Mets can find nothing wrong with Pelfrey's mechanics or his arm strength, and are instead focused on his mental approach to the game.

"That is a challenge for us as a staff," Manuel said of the mental part of pitching. "We have someone healthy, but we have other issues. That's a big challenge for us going forward. We're going to have to try and do all we can to get Pelf back on track on a consistent basis. We've got to find a way to unlock that, because this is not what we anticipated as far as his progression. You always expect there to be some bumps in the road for a young pitcher. But this one right here has just been kind of confounded."

Pelfrey's struggles remind the skipper of a similar period Jon Garland went through early in his career when Manuel was managing him in Chicago.

"He was probably a lot younger, but he still had that Major League experience behind him," Manuel recalled of Garland. "We threatened to do different things, send him to the bullpen. Matter of fact, I did pitch him out of the bullpen for a while -- got him back.

"But I notice when I reflect back on it, this period is one of inconsistency, which you don't want or hope for, but you just have to go through it. What I hope that happens is that toward the end here, these last couple starts, that we see a little better than what we have seen, because if we don't, then we begin to question the upcoming season. We believe that Mike Pelfrey is a franchise type pitcher. I believe that. I believe he has that kind of stuff."