The former midfielder is worried for Celtic's title chances.
Commons' future has been the subject of heavy speculation all season, with his contract up at the end of the current campaign.
And MacLeod fears Celtic will lose out big time if the 31-year-old is allowed to leave this January so that they can make a profit on any potential sale.
"Celtic are a poorer side without him, there's no doubt about that. He is the one player in the team who has got a spark. It could make the difference between Celtic winning and losing the league if Kris Commons leaves this month," MacLeod is quoted as saying by the Herald.
Celtic are currently second behind Aberdeen in the SPL table, although they have two games in hand over their in-form rivals.
Recently, meanwhile, Ronny Deila's side have been in Gran Canaria for a warm-weather training camp during their winter break, where they have also played friendlies against European opposition.
Commons has been used far less frequently by Deila than he was by the Hoops last season, with the Norwegian using a number of different options instead.
Celtic have struggled for goals at times but the hope among both staff and players is that they find their touch in front of goal when the league campaign resumes.