"At first, it was kind of minor, but it's bothering him now when he tries to reach out," Baker said.
Baker tried to keep Burton's status under wraps all weekend, so the Brewers wouldn't know.
The right-handed Burton started feeling sore during last Sunday's game against the Nationals. He was on the mound during an extended argument between Washington catcher Paul Lo Duca and umpires over a call.
"There was a little break in the action that took a while, and I didn't throw any," Burton said. "I got back in there and geared it up and felt just a minor strain."
Weathers pitched well on Friday and Saturday in Burton's place, throwing scoreless eighth innings in Reds wins over Milwaukee.
But on Sunday, in Weathers' second inning of work in the ninth, Bill Hall led off the frame with a single to right-center field. Mike Cameron followed with a bunt hit that had Weathers and catcher David Ross converging. After an awkward moment, Weathers made an errant throw to first base that allowed Hall to advance to third base. An intentional walk to Jason Kendall loaded the bases with no outs.
Closer Francisco Cordero took over, and with the infield and outfield playing in, pinch-hitter Craig Counsell hit a first-pitch sacrifice fly to right field that scored Hall with the walk-off run, which was charged to Weathers.
"I got to commend Stormy [Weathers] the way he pitched the last three days," Baker said after Sunday's loss. "He gutted it out because we didn't have Burton the last three days."
"Dusty is just trying to give me a little extra rest," Burton said. "I think it's good for me. I got a pretty good amount of innings in the first half. We didn't miss a beat. David stepped in and did a great job the last two days."
Burton pitched a perfect eighth inning in Chicago on Thursday, but it was a struggle.
"I felt like every pitch was all I could do to get it in there," Burton said. "It's not a good feeling with 2 1/2 months left in the season. We thought that the best thing to do was back off a little bit. I'm feeling a lot better. The guys in the training room know what they're doing, and they've got me feeling good. Hopefully, after the break, I'll be ready to roll."
Burton is following up a strong 2007 rookie season with another good year, so he would be missed if the injury lingers. In 43 games, he is 4-1 with a 2.23 ERA. His 48 1/3 innings lead the bullpen, and he has retired 33 of his 43 first batters.
Over his last 27 appearances, Burton has posted an 0.85 ERA (three earned runs over 31 2/3 innings).
Burton will spend his All-Star break in Cincinnati, so he can keep getting treatments and rehabilitate. The Reds will hold a team workout before Thursday's game.
"We'll make a determination if he's OK," Baker said. "If he's not, we'll DL him and get somebody here from [Triple-A] Louisville because they're home. That way when we backdate him, we'll pick up a week."