Since it's early in the season, the Brewers are playing it safe with their ace.
"If it was September, I would be out there," Sheets said. "I'm pretty sure I'm capable of pitching right now."
Milwaukee manager Ned Yost called Sheets' injury a "mild" strain. But Sheets raised some red flags when he told reporters he is having trouble pinpointing the source of the pain, and that he believes it is related to the torn "lat" muscle that abruptly ended his 2005 season and almost certainly contribute to shoulder trouble in '06.
Sheets started feeling tightness high in his triceps muscle in about the sixth inning of his April 12 start against the Mets in New York.
"I probably just re-aggravated that old injury a little bit," Sheets said. "I don't know -- they didn't really tell me anything. But that's what I speculate. ... There is soreness in the triceps; that's what was hurting in the last game. But I think it's caused by the soreness in the lat.
"It hurts. I ain't gonna lie. It hurts, but it's different than some of the 'hurts' I've had in the past. I feel like if I had to, I could go out and make my pitches."
Like Sheets, Yost said if it were September instead of April, the team may have taken a different approach.
"He definitely could pitch, but it doesn't make sense to pitch through it now," Yost insisted. "It's not like we've 'banged' him from throwing. He's going to do all of his throwing, all of his therapy work."
Sheets played catch for about 10 minutes in the Miller Park outfield on Monday afternoon under the watch of head athletic trainer Roger Caplinger.
Sheets made 34 starts and worked more than 200 innings in three straight seasons from 2002-04. In three seasons since, Sheets has averaged 21 starts and 134 2/3 innings while suffering from a variety of setbacks, including back, shoulder, finger and hamstring injuries.
But Sheets was off to an excellent start to 2008, the final season of a four-year contract with Milwaukee. He is 3-0 this season with a 0.96 ERA and 24 strikeouts vs. four walks.
Yost said he first considered pushing Sheets back one extra day to start Thursday's series finale against the Phillies, but he decided on a more cautious plan instead.
"I don't know if one day is going to alleviate the symptoms to the point where he isn't feeling it," Yost said. "I want him not feeling it when he steps on the mound."