"I've had this before. It's just tendinitis. It will go away."
Yost emphasized Sunday the current setback is separate from the injuries Sheets suffered last August and this March to muscles behind his right shoulder.
But Sheets said he believes it's related to healthy parts of his anatomy overcompensating for injured ones.
"A little bit sore is fine," Sheets said. "I don't need an MRI. I just need it to get stronger. Could I pitch today? Yeah -- but if I'm smart, probably not. I think if I can get on a roll, I'll be all right. But I can't even get going."
Dave Bush was notified Saturday night to be on notice for Sunday and started against the Dodgers on three days' rest. The Brewers are penciling in Sheets to start Thursday at San Diego, but they could scratch him again and instead go with Ben Hendrickson, who started Saturday's game against the Dodgers and would be right on schedule.
The Brewers knew Saturday night Sheets likely would be unavailable to pitch Sunday, but they did not announce the change until a few hours before Sunday's game.
"It really kind of manifested itself more since his last start," Yost said. "It was a little stiff when he went into his last start, but we thought we could loosen it up and get through it, and it didn't happen."
Red flags shot up last week when Sheets' velocity dropped significantly in his last start and he had none of his usual sharp command, but Yost denied at the time there was anything wrong with Sheets' shoulder.
The stiffness was not disclosed, according to general manager Doug Melvin, because it was not serious enough to send Sheets to the disabled list. The Brewers took a similar approach last month with reliever Dan Kolb, who left the team during a road trip to have an MRI scan in Milwaukee on his ailing elbow. After the scan came back negative, the team revealed the injury.
After the Brewers' 10-2 loss to the Dodgers, Yost apologized for the misinformation, saying he was simply trying to protect Sheets from the attention that was sure to follow any bad news about his shoulder. Yost said he never thought the injury would prove serious enough to prevent Sheets from starting Sunday.
Sheets spent five weeks on the disabled list late in his rookie season in 2001 with right rotator cuff tendinitis, and he was lifted from a start against the Phillies in 2003 with the same ailment.
He made 34 starts for three straight seasons from 2002-04, but he was limited to 22 starts last season, when Sheets signed a four-year $38.5 million contract that is the richest in franchise history. He missed five months early in the year with a rare inner-ear ailment that threw off his balance and awareness, then he tore the latissimus dorsi muscle behind his right shoulder in a start against Atlanta in August and missed the rest of the season.
This year, Sheets was on track for a fifth consecutive Opening Day start before he strained a different muscle in his upper back on March 9. He started the season on the DL, returned to action April 16 and appeared to be on track before his tough outing against the Astros.
"Believe me, it's not easy for me to not go," Sheets said. "But if you're pitching and it doesn't feel comfortable, it makes me want to puke every pitch. It's like, 'This don't feel right.'"
Sheets is 1-3 this season with a 6.64 ERA in four starts.
The Brewers already were thin in the pitching department because Tomo Ohka (shoulder) and Rick Helling (elbow) are on the DL.
Yost insisted the decision to skip Sheets on Sunday had nothing to do with the fact he has been suffering from an upper respiratory virus. Last year, a similar illness preceded a recurrence of an inner-ear condition called vestibular neuritis.
"He fluctuates on that," Yost said. "Sometimes he feels good, sometimes he doesn't."