The 22-year-old was ruled out for the first half of the campaign after suffering a freak pre-season injury that saw him hospitalised with kidney problems.
On Monday the former England Under-21s star took to Instagram to declare that he would be "back soon" after receiving some "good news", but Bruce says that any return is not imminent.
"Jack is back in the training ground and we're delighted to see him," he told the Birmingham Mail. "He's running a bit but he's got a long way to go.
"He's had a serious, serious injury so we'll have to be patient."
Grealish featured 31 times for the Villans in their first season back in the Championship last term, contributing five goals.