Jose Mourinho was sacked last week after United had won just seven of their 17 Premier League fixtured under the Portuguese manager.
Former United player Ole Gunnar Solskjaer was brought in on an interim basis and led the team to a stunning performance in the 5-1 win over Cardiff City on Saturday.
Merson feels the change in level of performance is ‘a joke’.
“The change at Man United is not down to Ole Gunnar Solskjaer. It is the players and it is a joke,” Merson told Sky Sports.
“You watch them on Saturday, and the difference was pathetic, a joke, embarrassing.
“I would be ashamed. All of a sudden Solskjaer is 100 times better than Jose Mourinho as a manager? Come on…. I do not like it.
“The players are all running around now, so I am going to go for a 4-0 win here (against Huddersfield on Boxing Day).
“They are grown-ups and they should have been able to go out and express themselves like at Valencia when they had nothing to play for. It is up to the players in the end…”