His contract will state how much notice he must give when resigning. That's his notice period to the club and is contractual. As in any business though, the business can decide to waive the notice period and tell him to go immediately. Such a decision (as is likely) could involve negotiation on how many weeks pay he's due under notice. He remains an employee of the club until his last working day, which will be mutually agreed. But I've not seen his contract, so dunno for sure.