The striker requires surgery on a ruptured Achilles tendon and has also been ruled out of Belgium's World Cup campaign this summer.
"It’s a terrible blow both for Christian and for the club,” said Lambert. “He will miss the rest of the season, obviously, and also the World Cup. But he’ll work hard because that’s what he does and he’ll come back for us stronger than ever next season.”
Aside from Benteke's injury, Karim El Ahmadi is a doubt with a thigh strain, while long-term absentees Jores Okore (knee), Libor Kozak (broken leg) and Charles N'Zogbia (Achilles) are out.
Felix Magath is targeting Saturday's trip to Villa as one of the four wins Fulham needs to maintain their Premier League status.
The German is Fulham's third manager this season, after Martin Jol and Rene Meulensteen, but the Craven Cottage faithful have seen no change in fortunes since his arrival in February as the club remains rooted to the foot of the table.
With 32 games played, Fulham is five points from safety, and Magath believes it needs four victories from its remaining six fixtures to avoid dropping into the Championship.
"I think that four wins are enough to stay in the league and, with six outstanding games, we are able to do that," the former Bayern Munich boss said.
That would appear to be a big ask of a side which has won just seven times all season, although its run-in sees it come up against just one team in the top half - Tottenham - which has shown inconsistent form in recent weeks.
This weekend sees Fulham visit Villa Park looking to reverse a trend of disappointing results on the road, with just two points taken from seven matches since a 2-1 win at Norwich City on Boxing Day.
Defeat could prove disastrous for Fulham, with four of its relegation rivals playing each other, but Magath insists his players will continue to fight for survival regardless.
"You are not really confident if you are losing games but at the training sessions they are concentrated," he said. "They are eager to do their job. I don’t think they have given up."
Fulham can take some comfort from the fact they are facing a Villa side that has been thumped 4-1 on its last two outings - at home to Stoke City and away at Manchester United.
Paul Lambert's men took an early lead in both of those matches before crumbling, and they have failed to find any consistency in the Premier League this season.
After a run of one point from four matches, back-to-back wins over Norwich City and Chelsea looked to have turned the tide before those two heavy losses dampened spirits somewhat.
Currently sitting 12th, eight points clear of the bottom three, Lambert's men look safe from the threat of relegation, but will be eager to take maximum points Saturday to kick start a strong finish to the campaign.
The visitors will be without Darren Bent, who is ineligible to play against his parent club, but Fernando Amorebieta is available again after serving a one-match suspension.
Magath said Thursday midfielder Scott Parker could return after a knee injury, but Kostas Mitroglou remains sidelined through a knee problem of his own.
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