The midfielder was sold to Liverpool in the summer for £40million and is set to face his former side this evening (7.45pm).
Oxlade-Chamberlain struggled for game time at the Emirates Stadium and moved away in search of regular football.
Wenger admits he did not want to lose the 24-year-old but reluctantly let him go when he realised he did not have the fight to battle for a starting spot.
The Frenchman also criticised his attitude and claimed he will never be a top player ahead of their reunion this evening.
“You can’t be a big player, sit in your rocking chair and say, ‘I do not want to fight.’ It doesn’t work like that. Every player has to fight,” Wenger said.
“I am convinced it is an important part of being a top player.”
Wenger offered the midfielder a new contract to stick around at Arsenal but he instead opted for a move to Anfield.
And now he may get a heated reception when he returns to his former side.
“In a big club, you have big competition with some good players. That is absolutely normal,” Wenger added.
“I didn’t want him to go. I offered him a contract to stay, but in the end he decided to go and we just had to try and get the best possible price.
“Look, he had one year to go. At start of the season we had four players with one year to go and I wanted him to extend his contract. Yes, he decided to go and we respect that. But at the end of the day I decided to sell one [of the four].
“We respect his decision and that’s absolutely normal and I have no problem with that. What’s important is that the players make a good career, preferably in your club. If it doesn’t happen, you still want them to have a good career.”
“That’s part of it, you know. If you look at the clubs, at any other club, we have more stability on the player side than any other club at the top level. Sometimes it happens with one player who we don’t want to go, goes.”