Boston ? Roger Clemens is headed for an MRI today to help determine the level of concern over his “fatigued” right groin.

However, the Rocket is planning to make his ’07 Yankees debut Saturday at the Stadium against the Pittsburgh Pirates. “He’s considering it,” general manager Brian Cashman said. “But I don’t want to get ahead of (the MRI results).”

Clemens, 44, was set to start tonight in Chicago until he felt the “fatigue” during a light throwing session Saturday. Cashman believes that Clemens’ problem stemmed from his last minor-league start, for Triple-A Scranton.

Rookie right-hander Matt DeSalvo will be recalled from Scranton and will start in Clemens’ place tonight.

Sunday at Tampa, Fla., Clemens was examined by Dr. Allen Miller. “Until we get the MRI back, I’d just be guessing,” Cashman said of Clemens’ return. “I know Roger’s optimistic.”

But Cashman’s worries are somewhat mitigated by his trust in Clemens.

“He really does know his body. He felt it’s something that’s no big deal,” Cashman said. “He wasn’t willing to call it a strain. There’s a great deal of trust because of our experience with him in the past.”

Until he participates in a major league game, Clemens, who is on a split minor league contract, doesn’t begin to get paid his pro-rated salary of $28 million.

Even if the MRI shows a cloudy picture, the Yankees have no intention of cutting ties with Clemens now.

“We feel we’re still in this thing,” Cashman said.

Still, Cashman added that Clemens is currently “no different than anyone else on a minor league contract there’s no guarantees.”

Manager Joe Torre confirmed that Saturday “is the day we’d focus on” for Clemens’ first start, but “it has (to come) from him.”

Johnny Damon expressed some disappointment in Clemens’ delay. “I think our team was definitely expecting (tonight’s start). But if he’s not right, it’s better for our team. He’s not just going to show up just to make the money.”

Said Torre: “We never really got to a point of feeling (Clemens) was here.”

DeSalvo, 26, is 1-2 with a 5.40 ERA in five games, four as a starter. He’s already faced the White Sox as a starter and lost, giving up four runs on six hits and four walks in 3$ innings on May 17.

And though Kei Igawa was another option to be recalled and start tonight, the injury Sunday to Doug Mientkiewicz allowed the Yankees to call up DeSalvo, who had been optioned out Friday.

Mientkiewicz will be officially placed on the disabled list today with a fractured right wrist and a concussion.