McLean, one of Melbourne's most consistent players this year, had further tests on Monday that revealed his injury was worse than initially thought.
"He saw the specialist very late yesterday afternoon and he needs surgery, which he'll have on Friday to repair ligaments," Melbourne football operations manager Ross Monaghan told melbournefc.com.au.
"That'll mean the recovery period is longer than a couple of months, so he won't be playing again this season, which is disappointing.
"Scans on Monday showed that he injured the ankle a bit more severely than first thought, so he needs surgery."
Monaghan said McLean's desire to play out the match despite the first-quarter injury was a show of courage.
"He was really committed to keep playing to help the team, as he normally is, and he desperately wanted to get out there and he thought if he'd done some damage, he couldn't do any more to it," Monaghan said.
"In his philosophical way, Brock is now refocused on getting the surgery done and the rehab done and focused on 2009."
