The Dutchman suggested yesterday that the England international is not up to the standard required at Old Trafford.
The 23-year-old joined the Gunners on transfer deadline day last Monday for a reported £16m fee following United's loan acquisition of Radamel Falcao from Monaco.
"Van Gaal has decided that if he is to bring Radamel Falcao in then Danny Welbeck is not going to play and Arsenal have bought a very good player," Redknapp said in this morning's press conference.
"It is the manager's decision and he has got more right than wrong so who can criticise him? Sir Alex Ferguson let players like Jaap Stam and Ruud van Nistelrooy go. You have to make decisions in this job."
QPR will take on United at Old Trafford on Sunday.