The Red Devils slumped to a disappointing 2-0 loss to Stoke City at the Britannia Stadium on Boxing Day as they stuttered to their third successive Premier League defeat.
Chelsea, meanwhile, were held to a 2-2 draw by Watford at Stamford Bridge in what was Guus Hiddink’s first game back in charge since Jose Mourinho’s sacking earlier this month.
Saturday’s defeat by the Potters placed Van Gaal under yet more pressure following United’s Champions League exit at the hands of Wolsburg earlier in December.
And former Arsenal star Merson is predicting another bad day at the office for United at Old Trafford in Monday night’s crunch clash.
Merson told Sky Sports: “It was another bad day for Manchester United on Boxing Day and with Chelsea improving, the roles have sort of been reversed.
“Chelsea, now under Guus Hiddink, are rolling along and I expect that to continue at Old Trafford, although the absence of Diego Costa through suspension is a big blow.
“I’m going for a clear away win by two goals to nil.”
United, who will compete in the Europa League last 32 next year, finished fourth in Van Gaal’s first season in charge at Old Trafford.
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