But while defeat would leave the Red Devils trophyless for a third successive season, it seems their European fate holds the key to Van Gaal's future.
Express Sport understands the 64-year-old could be sacked before the end of the season - like predecessor David Moyes - if and when Champions League qualification becomes mathematically impossible.
United are a public limited company listed on the New York Stock Exchange and their share price could be hugely affected by missing out on the Champions League.
Two years ago Moyes was sacked after just 10 months in the job when United's top-four hopes were officially over.
Jose Mourinho, sacked by Chelsea, is waiting in the wings to take over and is desperate to be given a chance at Old Trafford.
United's 3-0 defeat to Tottenham on Sunday and the subsequent reports of dressing-room dissent will not help the players against West Ham in the cup nor their top-four fight.
The club's American owners, the Glazer family, and executive vice-chairman Ed Woodward will make the final decision despite reports directors Sir Alex Ferguson, Sir Bobby Charlton and David Gill have a say.
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