Arsene Wenger has admitted Arsenal should have sold Alexis Sanchez last summer, even without the self-imposed requirement of finding a replacement.
The Chile international moved to Manchester United last month after a prolonged summer transfer saga saw Arsenal pull out of a proposed deal with Manchester City because a deal for Monaco's Thomas Lemar fell through.
And Wenger said the uncertainty over Sanchez and Mesut Ozil's futures with the club cast a cloud over the first club of the season, leading the manager to rethink his transfer strategy in the summer.
"We have not the defensive stability since the start of the season that you need to have to be completely efficient at our level," Wenger told BT Sport in an interview released to English newspapers.
"And as well there was a lot of uncertainty around the team with the Sanchez case, the Ozil case. For the whole season that was a really difficult case.
"In hindsight maybe despite the fact we couldn't have brought somebody in we should have cut that earlier.
"Sanchez, for him it was very difficult because as soon as he had game that was average he was questioned about his commitment and that is not his case.
"I never questioned his commitment but it was a difficult situation."
Meanwhile, Sanchez has told Sky Sports that he left Arsenal to Manchester United because he wanted to win trophies.
The Chile international has two FA Cup winners' medals to show for his three-and-a-half years at Arsenal. But after swapping the Emirates for Old Trafford in January, the 29-year-old says he is focused on winning bigger prizes.
"I came here to win," he told Sky Sports. "I left Arsenal because I wanted to develop and learn as a player and get to experience a new club.
"Manchester United are a huge club on the global stage. I came here to win everything. Otherwise I wouldn't have come here."
The former Barcelona man insists he chose the "biggest club in England" when he made his move, despite the earlier heavy links to both Manchester City and Chelsea.
Sanchez aded: "I think that Manchester United, since I was young -- and I'm not just saying this because I'm here, I'm an honest guy and I never lie -- I think it's the biggest club in England. That's what I think.
"There are lots of big clubs, and having played for Arsenal, they are also one of them. It's a huge club and I was there.
"But coming here, looking at the badge, I think United have to win everything because it's such a big club. The club crest says it all."
ESPN FC's Manchester United correspondent Rob Dawson contributed to this report.