Johnson told the Evening Post: "Bradley is at the stage where he can rejoin the group and I expect him to be training on Monday.
"It's taken a little time to get to the bottom of his injury and we decided we didn't want to take any silly risks, especially with the international break.
"He was still feeling it the other week and we left him out as a precaution at Forest. But he's since put it to the test and everything seems to be fine.
"He could have trained on Thursday, but we decided not to rush him. The lads are all having a three-day break and will be back to work after the weekend."