Okajima admitted Friday afternoon that he hass been bothered by various hip and back injuries this season, dating back to spring training, and it has caused hamstring issues.
Okajima spoke with Francona after Thursday's game and informed him of his discomfort, so the lefthanded reliever remained in Boston to receive treatment. He met the club in New York on Friday and is scheduled to return to Boston after the game for a couple of rounds of acupuncture before rejoining the team in Toronto next week.
Francona said Okajima's stay on the DL would be a minimum of a week to 10 days.
"I want to be back before the 15 days, but I can't say how long it will take," Okajima said. "I'll take the treatment and see how it goes."
Francona explained that Okajima has had difficulties getting used to the major league travel schedule, and even though earlier in the career with the Sox his numbers were solid, it's starting to take a toll on him.
"The travel in our league, when he first came over here especially, was shocking to him," Francona said. "Like the coast-to-coast stuff. His ERA was awesome, but it really affected him. I think the strain of how we travel, and the amount of travel, it has beat him up a little bit.
"Saying that, there have been a lot of little things with aches and pains, but everybody has to deal with that."
Okajima has struggled recently, giving up at least one run in three of his last four appearances since July 25. For the season, he has a 4-3 record with a 5.85 ERA and four blown saves.
When it became evident to Red Sox general manager Theo Epstein that he would not acquire a reliever at the trade deadline, the club decided to look internally. It was decided the Doubront would be moved to the bullpen for the remainder of the season.
"It's a little bit tough to change my routine," Doubront said. "It's a different routine, but I know I can do it. I want to help my team win and that's my mentality now."
The most difficult aspect of his transition will be learning how to warm up a lot quicker than he was used to as a starter.
"It's another step. I want to be here. I want to compete and I want to get outs," added Doubront. "I know I can do it. A reliever's job is to get guys out with men on base, and that's what I'm going to focus on. When the opportunities come, I'm going to do my job."
The Red Sox knew Doubront would be called upon at some point this season, but not this soon. The plan was to get him acclimated to his new role before given an opportunity.
"We were kind of hoping to lengthen that acclimation out a little bit more, but so much for development. 'Here are the Yankees, go get 'em, kid,'" Francona said.
The Sox also converted Michael Bowden to a reliever, but the reason Doubront got the call was because of his southpaw status.
"Having two lefties can really help," Francona said.
Doubront appeared in only one relief appearance for the PawSox, working two scoreless innings with one hit and two strikeouts.
In three starts with the Red Sox earlier this season he had a 1-2 record with a 4.11 ERA. It was during those starts when he realized he wanted to be back in the big leagues no matter what role he was in.
"I'm more comfortable," he said. "I know now I can pitch in the big leagues and I can get big league hitters out. [This new role] is going to be new for me, but it's the same game. All I have to do is pitch the way I know how."
Joe McDonald covers the Red Sox and Bruins for ESPNBoston.com. Follow him on Twitter.