26-year-old Maguire finally joined United from Leicester a whopping £80m transfer fee, after months of speculation surrounding his future.
Ahead of his debut, Merson was critical of the former Sheffield United and Hull star - claiming he would be out of his depth at Old Trafford, and wasnt in the same class as other top tier defenders.
"He’s not in Virgil Van Dijk’s class, is he? At Leicester, he played on the edge of his own box and had lots of protection from the players around him," Merson had said, as quoted by Leicester Mercury.
"But at Manchester United he will have to play on the halfway line and there will be a lot of space in behind him where he could get caught out for pace.
"I’ve seen good defenders have their careers ended by moves like that. They leave one team that plays a certain way for another where they don’t quite fit, and they get found out."
Man United used twenty-four (24!) different combinations in defence last season.Have they now found the definitive one? https://t.co/aD0VUwxerj
— 90min (@90min_Football) August 12, 2019
However, Maguires impressive debut saw him keep a clean sheet and offer some much needed sturdiness to Ole Gunnar Solskjaers back four, leading Merson to take back what he said.
"I thought he did very well. I thought I was very critical of him on Soccer Saturday, if Im honest, and I tried to get hold of him today, Ill talk to him tomorrow, he has text me back", Merson told Sky Sports The Debate on Monday night.
"What I wanted to say didnt come across in the way it should have. I thought it was a lot of money and I did, but I sort of didnt give him the credit he deserves with how good he is.
"I was a bit disrespectful in that way. He has played in a World Cup semi-final, he is an international and I was out of order and Ill be the first to admit that."