The Frenchman picked up the problem while on a run in pre-season and his boss had hoped that he might return by the end of the campaign.
However, the Scot revealed that the chances of seeing the 27-year-old in action before May are looking increasingly unlikely, although, in more encouraging news, defender Jores Okore is back in light training after his ruptured knee ligament and could return this season.
|ASTON VILLA LATEST
|25/1||Aston Villa are 25/1 with Bet365 to be relegated from the Premier League|
"It will be a big ask for Charles to come back this season because he's not had many games at all and that Achilles heel, as everybody knows, is a major issue."
On-loan Chelsea full-back Ryan Bertrand, meanwhile, feels that Sunday's 4-1 win over Norwich City was a marker for what the side can achieve between now and the end of the season.
"A win does wonders for the club," he enthused.
"We're in an okay position now so we have to keep focused and keep it going for as long as we can.
"We've had a mixed bag of results but it's important that we've been able to get a good win just before the break and hopefully we can take that into the next game."