The Chilean was sold by Barca to Arsenal in 2014 and faces up to the Blaugrana for the first time since his departure in Tuesday's last-16 first-leg clash at the Emirates.
Wenger said he will speak to Sanchez before the match to make sure he is in the right frame of mind to play his best football, per Jamie Anderson in the Daily Star:
He will be fired up, but that doesn't mean he will be in the right zone. The performance zone is where you are focused and relaxed and that is what is difficult in sport. Sometimes when you are too focused you are not relaxed, so it's a zone where everything looks easy and sometimes when you play against your former club you are not necessarily in that zone.
[I will have] a little word, yes. He can help us to win the game. But I know that not one player will win us the game. We need a top level team performance where everybody is spot on in the discipline and sharp physically and ready to work for the team. If everyone does that then maybe Alexis can make the difference but it's not especially on him. We need all our players.
Sanchez never quite nailed down a first-team spot at Barca and, despite netting 19 goals and providing 10 assists in the 2013-14 season, was sold to Arsenal for £35 million in July 2014, per WhoScored.com.
He has since become a vital part of the north London side's attack and will need to be at his very best against Barca if Arsenal are to beat the side currently ranked as Europe's best by Bleacher Report's Sam Tighe:
It is vital that the Gunners take a lead with them to the Camp Nou for the second leg if they are to avoid a last-16 exit in the Champions League for the sixth season in succession.
Arsenal's chances of keeping a clean sheet are minimal, meaning they will have to score at least twice if they are to win the opening leg.
He will undoubtedly be desperate to get one over his former employers, but Wenger is clearly eager to make sure the 27-year-old does not lose sight of the main aim.
Arsenal are huge underdogs to advance from their last-16 tie against Luis Enrique's side, but a victory at home would give them a chance when they go to the Camp Nou in three weeks.
The only way the Gunners are going to claim a win is if their defence is tight, and Sanchez, Olivier Giroud and Mesut Ozil are all on top form in attack.
It will be Wenger's responsibility to make sure they are all in the right frame of mind, but the manager can do little once the action gets under way, and he will have to trust that his star forwards can show their best form.