"The ones who have been called in were injured for significant periods of time last season. I'm expecting eight of them to start working with me on Tuesday," Blues coach Mark Bowen told the Birmingham Evening Mail.
"They will be working hard next week. Hopefully, it will give them that platform to join in with the others when they come back the week after.
"It's more endurance than anything. The bigger players physically are the ones who take a lot longer to pick up their fitness.
"Olivier's operation went well and, in fairness, if we had been fighting for our lives in the last two or three games of the season, then we might well have chosen to throw him in.
"But he has been working already and Clinton Morrison's shoulder has cleared up as well. He had one or two slight problems but he should be okay for the build-up to the season.
"Don't forget, we have got a game against Newcastle towards the end of July in the Asia Cup and that gives us less than two weeks to try and get the players match fit. It's a massive task. What we are trying to do is give some of them a head start."
