Delcarmen had been sidelined since July 1 with a right forearm strain. He threw nine pitches in a Minor League rehab game Thursday.
His absence was felt during Friday night's loss when Fernando Cabrera, who was on the roster for one day, surrendered a grand slam to Bengie Molina in the top of the fifth inning.
"I hope it will be really good," said Red Sox manager Terry Francona. "He's a guy that, when he's going good, has the ability to go multiple innings, get lefties, righties. That's been missed a little bit the last couple of weeks. Hopefully it will be a very valuable, getting him back. The way he can pitch is important, but it should really help."
Delcarmen is encouraged by the improvement of his health.
"I feel real good," Delcarmen said. "My arm feels normal. With the All-Star break, it helped out a bunch. I just did all the treatment and my forearm feels great, my shoulder feels awesome, so go get 'em."
Buchholz strained his left hamstring running the bases at San Francisco on June 26 and had a successful rehab start for Triple-A Pawtucket on Friday night, throwing 60 pitches and allowing two runs over 3 2/3 innings.
"I expected to be a little bit rusty," said Buchholz. "I basically went in wanting velocity and everything to be there, and not notice that I was favoring anything, so that's what I went out there to do. Everything felt good.
"I just left a couple pitches in the middle that got hit. Release point was a little scattered. But other than that, it went well. Everything felt good. The pitches felt good coming out of my hand. Each pitch that I threw, I threw a couple good ones. Stuff's still there. I just wanted to make sure there was nothing wrong."
With Buchholz now set to return, lefty Felix Doubront, who filled in for him the last two times in the rotation, was optioned back to Triple-A Pawtucket.