The forward impressed upon his return to Fir Park on a short-term deal in the second half of last season and is set to put pen to paper.
McFadden, 30, featured as a trialist in a friendly against Newcastle earlier in the week and McCall is thrilled to have the player on board for the forthcoming campaign.
He said: "It will be done either this afternoon or first thing in the morning.
"Everyone knew the situation with James, he was coming in to get games under his belt and he did well so we thought it might be farewell at the end of the season.
"He's had a few things to weigh up but I think he's more than happy to sign a deal here and get some football under his belt and thrive at what is a good club for him.
"Obviously he's good for us as well."
Asked if the capture of the Scotland international is a major coup for the club, McCall added: "A player of his quality, it is.
"He did really well for us last season and showed his quality.
"He's just needs to get his sharpness back. He's missed a little bit of pre-season.
"But it will be a great signing not only for ourselves but also for Scottish football to have a player of his ability and talent."