Sheffield had already missed the Mets first two games of their four-game series against the St. Louis Cardinals and will likely be out until Friday when they play the Yankees. Manager Jerry Manuel said Sheffield was available to pinch hit in an emergency but there was no plan to place the slugging outfielder on the Mets' crowded disabled list.
"The best scenario is the route we're taking right now," Manuel said. "If we can get these two days he should be ready to go."
The 40-year-old Sheffield is tied with the injured Carlos Beltran for the team lead with eight homers and is hitting .387 in his last eight starts.
Sheffield described the injury as being in the area similar to where shortstop Jose Reyes hurt his hamstring, and that he had fluid in the bursa sac in the knee. He said it should take one to two days for the pain to subside.
"Just to be able to go out not 100 percent, that's not good enough for me," Sheffield said. "We're doing everything that we need to do now. The most important thing is that I'll be back on the field in a day or so."
To add a position player to a bench that has shrunk considerably with Beltran, Reyes and Carlos Delgado sidelined, New York purchased the contract of infielder Argenis Reyes from Triple-A Buffalo and designated left-hander Jon Switzer for assignment.
Reyes batted .218 in 49 games with New York last season and was hitting .296 with one homer and 13 RBIs at Buffalo.
Perez, out with right knee tendinitis since May 3, threw 50 pitches and said his arm felt strong and that he didn't think about his knee while throwing all his pitches.
"I just have to work up to 100 pitches," said Perez, who will make at least one more minor league start before being activated from the DL.
Maine, who has not pitched since June 6 because of right shoulder weakness caused by a pinched nerve, threw about 40 pitches and said he had some achiness but was pain-free. He felt he needed one or two more outings before coming off the DL.