Curtis Fleming has admitted there is still no timeline on George Tanner's return to action and ruled out his recovery in time for the game against Birmingham on March 5.
The full-back is taking part in some light training as he continues his rehabilitation from a hamstring injury picked up in the home defeat to Queens Park Rangers at the end of December.
Manager Nigel Pearson has previously given a two-month timeline for Tanner's recovery, meaning the club were hoping to get him back in action at the beginning of March.
But City assistant Fleming admitted that while Tanner is training "harder than ever" they are continuing to remain cautious with his road to recovery.
When asked whether a return on March 5 was realistic, Fleming said: "No, it's not realistic. For us at the moment we still want to make sure that he's right and to make sure - he knows his body.
"There's a gradual build - we want him back and he's training harder than he's ever trained. He was at the academy at Manchester United where they undoubtedly trained him hard and at Carlisle where they trained him hard and here's the same.
"We're going to get you (Tanner) where you think you can go and at the moment we're working really, really hard on that. As soon as he's ready he'll come back in."
There was also no positive update on Rob Atkinson who was also plotting a comeback at the beginning of next month. The centre-back has been dealing with a calf injury that forced him off against Cardiff just over a month ago.
"We're still waiting for these guys," Curtis added. "They're still not training with us just yet so again we're counting down slowly but surely, we want them all back fit and ready to go.
"We have to make sure there's no breaking down with them. We have to understand that George came from League Two football and Rob League One so this is a different intensity to play."
With midfielder Matty James expected to make a return for the final 10 matches of the season - starting with a trip to Blackburn Rovers on March 12 - and Andy King out long-term, the club are remaining cautious with Joe Williams' fitness following his return to action.
He played 80 minutes against Middlesbrough on Tuesday night meaning Pearson was forced to rest him against Coventry. He hasn't started back-to-back matches since the end of November.
Fleming admitted it won't be long until Williams will be starting week-in-week-out but emphasised the importance of remaining patient.
He added: "He understands what we're doing. The medical team have done brilliantly with him and he has to be honest with us about his body and how he is feeling.
"We are gradually building on that for him and we want him to be available for every game for 90 minutes and that's what he wants, he's chomping at the bit. We are managing it and the medical staff too so we will get that (fitness) sooner rather than later we hope, we will be careful with him.
"It's not short-term this, he's going to have a huge part to play for Bristol City in the future so we try and get him in the best shape as he can be."
Pearson is expected to have the same squad to work with for Saturday's trip to Nottingham Forest.
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