Sheffield is recovering from two cortisone shots in his shoulder that he received after being removed in the eighth inning of Sunday's 11-1 victory over the Red Sox. He has been playing with bursitis and a separated muscle in the shoulder for much of the season.
Despite playing regularly in pain, Sheffield has been a reliable producer in the Yankees' vaunted offense. The AL MVP candidate is batting .297 with 35 home runs, 116 RBI, and a .400 on-base percentage.
"I can't put into words what Sheffield has meant," manager Joe Torre said. "He's special."
Torre decided several hours before Monday's game to rest Sheffield.
Sheffield said he would not have gotten the two shots Sunday if the Yankees hadn't taken two of three from Boston over the weekend. New York's lead over Boston in the AL East stands at 4½ games.
When he plays again, Sheffield said Sunday, "just depends on how I react to it. Right now, I don't have any feeling in my shoulder. I missed three games last time, hopefully it's different this time."
Torre said he'll see how Sheffield is feeling Tuesday before deciding whether he plays that night against the Blue Jays.