"I think it's a good investment because we are talking about a top player and I'm hearing that the amount is around £20m".
But having previously said he still wanted Sanchez to stay as well, the Arsenal boss seems to have given up all hope of keeping the Chile worldwide.
The United manager said last March that he never would have let Hernandez leave United if he had been in-charge when the player was at Old Trafford.
Meanwhile, Jose Mourinho has shared his thoughts on the "phenomenal" player.
Arsene Wenger has spoken out about the various transfer rumors surrounding Arsenal star, including a move to Manchester United.
The Premier League leaders have always been linked with signing the Chilean forward, and had a reported £60m offer for him accepted by Arsenal on deadline day last summer.
"You look at Manchester City and they're so far ahead of everybody else, not just in points but in the way and style they play".
United is said to have presented Arsenal with a bigger offer than City, and although Mourinho claims it was not in the club's plans to sign players in January, he acknowledged that fantastic opportunities are worth pursuing whenever they present themselves.
Sanchez's older brother Humberto arrived at Heathrow Airport on Saturday with a number of family members in preparation for the player's departure from Arsenal. "If somebody speaks of one of my players to tell we are interested, I wouldn't be very happy".
"I think when a person insults another, you can expect a response or you can expect contempt, silence", Mourinho said.
Is it not City and United maybe want him and he will consider all elements in the round before making a decision? I don't want to give you wrong information.
Playing with Raheem Sterling on the wings either side of Sergio Aguero and Gabriel Jesus, Sane has been in devastating form this season. We appreciate what a good player he is.
Part of him wants to stay at PSG because he believes they have a genuine shot at winning the Champions League this season.
Obviously, if Sanchez leaves in the summer, Arsenal will receive nothing in return, so it's certainly in their best interest to sell him now.