Wakefield, 11-3 with a 4.31 ERA, has been out since July 18 with a sore back that has led to nerve irritation in his left calf, forcing him to walk with a limp.
The 43-year-old knuckleballer made his first minor league rehab start on Saturday, allowing two runs and three hits in 3 1/3 innings with Triple-A Pawtucket.
Boston, which has won just five of 14 games and is still without right-hander Daisuke Matsuzaka, had hoped Wakefield would be able to rejoin the rotation later this week. But manager Terry Francona said there was a "pretty good chance" Wakefield would make another Triple-A rehab start Friday.
"This is a tough decision to make because we all think he can help us on the mound," Francona said. "But there's some other issues involved, like fielding your position, is he going to get weaker, is he going to hurt himself in another area. So we'll do the best we can.
"We all know what's wrong with him," Francona added. "At some point he's probably going to need a surgery. If he has the surgery this week, we're probably not going to have him available next week. We're trying to figure out what to do."