Sheffield said it's been bothering him on and off for a couple of weeks but he decided to play through it with New York dealing with a rash of injuries and a flu bug that swept through the clubhouse.
"I'll be able to play," the outfielder said. "I just want to be able to explode like I want. I'll be able to get the job done."
Sheffield homered in the first two games of the Subway Series and went 2 for 3 with a walk in Sunday's 15-0 loss against the Yankees. The 40-year-old slugger is batting .270 with seven homers and 24 RBIs in 52 games this season.
Sheffield could stay out of the outfield for the first part of this week, too. The Mets are off Monday before opening a three-game set at Baltimore on Tuesday.
"I think the DH, this has come at a good time for us," manager Jerry Manuel said. "No question."
Sheffield, who said he doesn't know when he's going to get the test, signed with New York after he was cut by the Detroit Tigers on March 31. The nine-time All-Star hit his 500th career homer in the Mets' 5-4 victory over the Milwaukee Brewers on April 17.
Also, the Mets announced before their game against the Yankees that they had acquired minor league infielder Javier Castillo from the Chicago White Sox. The club assigned Castillo to Triple-A Buffalo and released outfielder Jason Cooper to make room on the Bisons' roster.