Clay Buchholz’s next scheduled turn in the Boston Red Sox’s rotation is uncertain after his shaky outing Monday.

Meeting with the media before Tuesday night’s game in Atlanta, Red Sox manager John Farrell would not commit to Buchholz starting as planned this weekend. Farrell said he was worried about Buchholz’s left knee, which the manager said was hyperextended on a pitch after the right-hander ran the bases at the National League park, in addition to Buchholz’s severe weight loss in the Memorial Day heat.

“He lost seven pounds (Monday), which for Clay is unheard of,” Farrell said. “It’s the first time he’s dealing with the heat and humidity this year. We’re in May. It’s not really all that hot yet, but it’s different than the weather we’ve been involved in. That’s not going to be used as an excuse, it’s just a condition that everyone’s playing in here.”

Buchholz was roughed up for six runs on four hits and eight walks in three innings before the Red Sox rallied for an 8-6 win over the Braves. He has a 2-4 record with a 7.02 earned run average on the season, and he is winless in his last four starts.

“We met with him a little while ago,” Farrell said. “We’re undetermined with his spot coming up in another four days. We’ve got to get through (Wednesday’s) bullpen. After he ran the bases (Monday), there was a pitch where his landing leg gave out, so we’ve got to make sure that he gets through his bullpen (Wednesday) that that knee, where he felt like it was a little hyperextended, doesn’t persist or show any further soreness. So that’s where we are right now with Clay.”

Depending on the outcome of the bullpen, Farrell said, the team will determine if Buchholz can take the ball. Farrell added that the knee and the weather should not be used as a crutch as the Red Sox continue to evaluate what is wrong with their valued starter, who was one of the best pitchers in baseball for the first several months last season.