McKinnon, who starred in his debut campaign with the club last year, suffered what was originally expected to be a season-ending knee injury in a trial match in February.
However, his recovery from a knee reconstruction has been such that the club's medical staff have suggested he could be back in action in 2008.
Cleary said today that it was a case of wait-and-see as far as when McKinnon would be available for selection again.
"It's bit hard to tell, but his rehab is going really well and all we can do is keep monitoring that," he said.
"If he continues that way, he might be a chance, but it's not something you want to bank on. You don't want to get your hopes up. We'll just cross our fingers and see what happens."
Team doctor John Mayhew said McKinnon had made much better progress than expected.
While Mayhew couldn't give a date for a comeback, there was optimism that it could be late in the season.
McKinnon and skipper Steve Price gave the Warriors a boost before the Auckland-based club recorded their first away win of the season with an 18-16 result over Newcastle on Saturday night.
Both have extended their contracts, with McKinnon, 27, adding two years to his to take him through to the end of 2011.
Price, 34, signed up to lead the Warriors for a fifth season next year.
The prop has had two games back after two months on the sidelines with a hamstring injury that ruled him out of the Queensland squad for State of Origin 1 last month.
He made his 285th NRL appearance, and his 63rd for the Warriors, in the match against Newcastle.
Cleary said McKinnon and Price's decision to extend their contracts had given the club a fillip.
"Everyone realises those two guys had a fantastic season last year and we've played almost the whole season without them to this point," he said.
"They're a really big part of our club and the future, and to have them locked up is a real boost."
Price's injury in the opening-round defeat to Melbourne and the length of time he was out had raised doubts about whether he had a 16th NRL season in him.
Cleary said how Price himself felt was always the key issue.
"Seeing him injured in the first week put that on the backburner," he said.
"He got through his rehab really well and when he set foot back on the field he was pretty happy with how it went. That was pretty much all we needed."
The contract news concerning McKinnon and Price followed the decision of Brisbane winger-fullback Denan Kemp to commit to the Warriors for the 2009 and 2010 seasons.
Kemp's signing was announced on Friday and the 21-year-old showed that night why the Warriors were interested in him.
The former Australian junior football representative grabbed four tries, including the winner, in the Broncos 30-26 victory over Parramatta, taking his season's tally to nine in nine matches.
"Four tries isn't bad, is it? Cleary said.
"He's a talented youngster and we're looking forward to him being a part of us next year."
Links:
[1] http://www.odt.co.nz/files/story/2008/06/league--cleary-cautious-over-early-return-for-mcki-1.jpg