Sanchez was understood to be on the brink of a move away from Arsenal last summer only for his prospective switch to Manchester City to break down at the 11th hour when the Gunners were unable to source a replacement.
The Chilean's commitment and attitude have been questioned in some quarters throughout this season - particularly once his move to United grew closer - but Wenger has leapt to the defence of his former player.
"Sanchez is a great guy and he has always been committed," he told reporters at a press conference.
"I'm not worried about [Arsenal's status in the game taking a hit]. When players get to a certain age and want to go you have to respect that.
"He is 29 years old, it is maybe his last contract. Financially it's important. He could combine both. He's going to a great club."