Allardyce hopes the return of Seamus Coleman, Phil Jagielka and Leighton Baines will help cover the Frenchman's absence ahead of Everton's trip to Burnley in the Premier League on Saturday.
"Mangala will be out for a bit longer than first feared," Allardyce told reporters.
"We assessed the scans and we've seen there is a little bit more damage than expected. I think it is highly unlikely we will see him again this season.
"Bainesy and Seamus are both back, which is important to us. Jags is back too."
Allardyce arrived at Everton in November on an 18-month contract and made an instant impact to lift the relegation-threatened outfit up to ninth in the league standings.
British media reports say Everton are already lining up a new manager for next season, which comes as a surprise to the former England manager.
"I am here as long as I win football matches, and if you don't win football matches it doesn't matter how long your contract is," Allardyce added.
Everton have collected two wins and a draw in their last three home league matches but visit Burnley with just one league win on the road so far this season.
Michael Keane returns to Turf Moor for the first time since securing a move to Merseyside at the start of the campaign, with the defender "desperate" to help Everton rediscover away day success.
"The lads are desperate to do well away from home. I think, even though the result wasn't good at the weekend (against Watford), the performance was a bit better than it has been away from home lately," the 25-year-old told the club website. (www.evertonfc.com)
"We know it is going to be a tough game, we know what to expect from Burnley. Hopefully we can go there, impose our game on them and get the three points."
(Reporting by Hardik Vyas in Bengaluru, editing by Pritha Sarkar)
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