Barton has been offered to Everton this week.
"If Joey Barton went to Everton, knuckled down and played his best football he would be an asset," he told talkSPORT. "The problem we've always got with Joey is that we just don't know [what he might do].
"If it was me, and I was manager, there would be too much of a doubt about him. I wouldn't entertain it."