The 70-year-old introduced the highly-rated Frenchman into the Red Devils' first team fold last season but has failed to convince the teenager to sign a new contract.
Speaking to MUTV, Sir Alex revealed "Pogba signed for Juventus a long time ago as far as we’re aware. Which is disappointing.
|21/10||Manchester United are 21/10 with Sportingbet to win the Premier League next season.|
"I don’t think he showed us any respect at all so, to be honest, I’m quite happy that if they carry on that way, they’re probably better doing it away from us.”
The future of promising left-back Ezekiel Fryers also remains in doubt but Sir Alex is expecting the youngster back for pre-season training.
"We haven’t heard anything from Zeki Fryers I don’t know what’s happening there but he’s not been in touch with the club,” he added.
“His agent hasn’t been in touch with the club and I can only assume he’ll be back for training today."