Louis van Gaal has claimed Danny Welbeck was good enough only to be a substitute at Manchester United, and insisted he does not regret sanctioning the England forward's £16m exit from Old Trafford.
In a robust defence of his decision to sell Welbeck, Van Gaal said the 23-year-old was "more a substitute than a line-up player" and the forward's ongoing presence at United would block the progress of teenager James Wilson.
Welbeck faces his former club for the first time this evening since his move to the Emirates Stadium in September.
The England striker has scored 10 goals for club and country since leaving United, his form is a stark contrast to the injury-interrupted displays of Radamel Falcao.
But despite Welbeck's performances for Arsenal, Van Gaal insists he does not need to justify his decision.
"I don't have to prove that (I was right)," said the United boss. "Why do I have to prove that? I have already said what I think - he was not a line-up player, he was more a substitute than a line-up player.
"He was already, with different coaches, not a line-up player, but then with Mr Van Gaal, the world is changing? No, the world is not changing. They are the facts.
"They are not my facts, they are the facts of Danny Welbeck and we have (Robin) van Persie and we had Wilson, and when you keep Welbeck, then you don't give any chance to youngsters and that is our philosophy.
"And then also we could buy Falcao. When that is not enough reason then I don't know what is - then I'm not a very good manager."
Welbeck's success at Arsenal has coincided with the player being deployed in a centre-forward role by Wenger, a position he was largely denied at United by the presence of Van Persie and Wayne Rooney.
Ironically, Wenger has now admitted he will move Welbeck to a wide position in order to accommodate the fit-again Olivier Giroud in his starting line-up. "I think you have players who play on the flanks who score goals," said Wenger. "I don't think that will stop Danny from scoring.
"Cristiano Ronaldo played all his life on the flanks and scored more goals than games he played. What is a problem for him is to play. He is adaptable, the modern player is adaptable. Alexis Sanchez can play wide left and wide right as well as through the middle. Welbeck as well.
"Louis Van Gaal did not have Welbeck under his orders for a long time. It is always difficult to know players well in three or four weeks. Rooney and Van Persie had an exceptional record, so he had two outstanding players in front of him. What he needed was a chance."
Falcao, Welbeck's replacement, is facing a further two weeks out with a calf injury. And Van Gaal has admitted United's decision to sign him on loan from Monaco, rather than a £45m permanent deal, was due to concerns over his recovery from a cruciate ligament injury sustained in January.
Asked if Falcao can justify United's decision to sign him, Van Gaal said: "I hope so. That is clear I think, but do you think that we expected he would be so many weeks injured?
"Yes we knew of his injury, but because of that, maybe we didn't buy him."
(© The Daily Telegraph, London)
The last time Arsenal and Manchester United faced each other with both clubs outside the top four of the Premier League was 16 years ago, and to give you a historical perspective on that Sunday at Highbury in September 1998, the first goal was scored by Tony Adams, whose statue now stands outside the Emirates Stadium.