Youkilis, who is not on the disabled list, missed his fourth straight game Saturday, and five of the last six, with tightness in his right quadriceps.
"Basically, rest was the only thing that was going to help it out," said Youkilis before Saturday night's game. "I've got to strengthen it and fix it."
The first baseman said that the rest is helping.
"It's getting stronger, day by day," Youkilis said.
Francona said that he decided to just rest Youkilis and not put him on the disabled list because the team didn't think he needed 15 days to recover.
"You DL him, and then he doesn't need the last seven days, you lose him for seven days," said Francona.
But that means Boston is playing shorthanded, with only 24 players available on the active roster.
Youkilis said in addition to rest, he's stretching and doing strengthening exercises. He's Boston's leading hitter this season with a .329 average, and he has hit nine home runs and 44 RBIs.
"I've hated to have him out of the lineup," Francona said.
Eric Hinske was in the lineup at first base on Saturday.
Schilling, Donnelly updates: Francona said Curt Schilling, on the disabled list with tendinitis in his right shoulder, threw before Tuesday's and Wednesday's games.
"I think he's making very good progress," the manager said.
He added that Schilling will also be checked thoroughly by team medical personnel when he returns from the All-Star break on Wednesday night, and more extensively on Thursday.
Francona also said that reliever Brendan Donnelly, on the the disabled list with a strained right forearm, will throw a bullpen session for the first time on Tuesday.
When Donnelly is nearly ready to return, Francona said he will likley be sent on a rehab assignment to one of the team's Minor League affiliates.
"One, to make sure he's sharp," said Francona. "And two, when he comes back, [we want to] make sure he's completely healthy."
Connection with Leyland: Francona said Tigers manager Jim Leyland got to know his father, former big leaguer Tito Francona, well when Leyland managed in Pittsburgh.
The Red Sox skipper said that whenever Leyland sees him, he always first asks, "How's your father doing?"
"Jim had the ability to make my father feel seven feet tall," Francona said.
Okajima rewarded: Reliever Hideki Okajima, who is headed to the All-Star Game in San Francisco on Tuesday ater winning the American League 2007 Monster All-Star Final Vote, received an appropriate gift from a sports program in Japan.
A reporter from the show presented Okajima with a basket of star fruit. The presentation was taped for broadcast in the Red Sox dugout at Comerica Park.
It is called star fruit because when you cut it in the middle and open it up, the inside looks like a star.
Up next: The Red Sox and Tigers conclude the three-game series and the first half of the season on Sunday at 1:05 p.m. ET, when righty Daisuke Matsuzaka (10-5, 3.53 ERA) faces Detroit lefty Nate Robertson (4-6, 4.86).
Paul Harris is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.