Sheets suffered a strained right groin after his final pitch of the third inning, and the Cubs went on to avert a three-game sweep and snap Milwaukee's four-game winning streak.
"Groins are something you don't mess with," said pitching coach Mike Maddux, who suffered two similar injuries during his own playing career. "Your upper half relies on your lower half. Benny is a thick-bodied guy, and his legs are his game. [Exiting] was absolutely the best thing he could have done right there. Don't give it a chance to go bad.
"Hopefully, it's an 'owie' that gets taken care of quick before it turns into an injury."
After a rain-delayed start and in 44-degree weather, Sheets worked three scoreless innings and surrendered four hits. He felt something "grab" at the top of his right leg when he spun and watched Derrek Lee's inning-ending groundout in the third inning, and Elmer Dessens quickly began throwing warm-up tosses in the bullpen while the Brewers went down in order in the top of the fourth.
Dessens surrendered five unearned runs in his only inning of work and took the loss. Sheets remained winless in four starts since a complete-game victory over the Dodgers on Opening Day.
"It was just bad timing for today," Sheets said. "It was bad timing for our bullpen, and to have a three-inning start, that really hurt."
Like Sheets, Maddux pulled the groin at the top of his right drive leg on two occasions. One of the pulls was minor and he tried to pitch through it, but the problem persisted.
Sheets said his own injury history contributed to the decision to call it a day. Back in August 2005, he felt a tweak behind his right shoulder in a game against the Braves, but "let it go" for one more pitch. Sheets tore his latissimus dorsi muscle on that curveball to Chipper Jones and missed the rest of 2005 and more than two months of 2006 with related injuries.
"There was really no sense in pushing through it and taking that chance right now, especially this early and with the weather as it was," Sheets said.
After fighting injuries for the last two years, does Sheets find himself asking, "Why me?"
"Naw, that kind of bums me out," he said.
Sheets' next scheduled start is Monday against St. Louis at Miller Park. Because Thursday is an off-day, should Sheets need to miss a turn in the rotation, the other four starters could pitch on regular four days' rest.
Brewers manager Ned Yost hopes to know more about Sheets' condition on Friday, when the Brewers open a series against the Astros at Minute Maid Park in Houston. The team is off Thursday.
"There's nothing I can do about it right now," said Yost, who was slow in packing up his belongings because of a cracked right collarbone he suffered on a jog the day before. "It's not something I'm going to stress about on the off-day. We'll wait and see."
Sheets stayed positive.
"I don't think it seems severe at all," he said. "I could see it coming down to two days, but what do I know? [The medical staffers] seem to think the same thing."
Adam McCalvy is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.