The Scotland international returned to Fir Park for a six-month spell in 2012/13.
He signed for Well in January in an effort to prove his fitness - following an injury-ravaged end to his time at Everton.
McCall was happy to welcome the 30-year-old back to the club that helped to launch his career and remains convinced that he has plenty to offer.
McFadden netted from the penalty spot as Motherwell suffered a 4-2 friendly defeat to Newcastle United on Tuesday and is ready to commit himself to the club for the foreseeable future.
McCall said: "He will be in tomorrow to sign.
"I'm led to believe it's going to happen and, if it does, it will be another good addition to the squad.
"Once he's done it, it will be a shot in the arm for the fans."