Celtic allowing Craig Gordon to leave the club has been the "biggest mistake" of the season claims pundit Alan Rough.
The 37-year-old keeper left Celtic in the summer after six trophy-laden years, heading back to Hearts for a second stint with the Jambos.
The club opted to sign flop Vasilis Barkas in a big-money £4.5m transfer deal but the Greek stopper has failed to fight off competition from Scott Bain and Conor Hazard.
In stark contract, Gordon has been a major success for the Championship winners and earned a recall to Steve Clarke's Scotland squad.
Former Parkhead goalkeeper Rough told the PLZ Football Show that the difference between the sticks for Celtic and Rangers has been a major difference this season.
Allan McGregor was again the hero for Steven Gerrard's side as he stopped Odsonne Edouard's penalty in the 2-0 win over their rivals.
Rough said: "Who have we been saying is the man of the match in the last three Rangers and Celtic games? Allan McGregor.
"That sums it up for me. He might not have a lot to do but he makes the saves.
"As soon as Celtic fell into the trap of letting Craig Gordon go in that area, I don’t know why they didn’t keep him on. That for me is the biggest mistake.
"The big goalkeeper, in the big games, like Allan McGregor wins you the games whether you are playing well or not."
