The Red Devils had a relatively quiet window compared to their rivals, as they missed out on top target Jadon Sancho.
However, United did bring in £40 million midfielder Donny van de Beek, and on deadline day sealed deals for Edinson Cavani, Alex Telles and youngsters Facundo Pellestri and Amad Diallo, with the latter set to arrive in January in a deal rising to £37m.
Their top-four rivals Arsenal made a late push to sign Partey from Atletico Madrid as they activated his £45m release clause, and Gunners legend Merson is unsure why United, or even Manchester City didn’t attempt to bring in the Ghana international.
‘I don’t know why Manchester United or even Manchester City didn’t go for him. He’s better than what they’ve got.’
Jose Mourinho returned to Old Trafford to inflict a humiliating 6-1 defeat on his former club last weekend.
Ole Gunnar Solskjaer’s side will get the chance to bounce back when they face Newcastle United at St James’ Park after the international break.