Dalton Bell is the Argonautsí starting quarterback.
Argos head coach Jim Barker will make the announcement on Tuesday following practice.
Cleo Lemon, who started 12 games as the Argos compiled a 6-6 record, suffered a concussion during Touchdown Atlantic on Sunday afternoon in Moncton. The Argos lost 24-6 to the Edmonton Eskimos.
Itís believed, though, that Barker was going to make the change even if Lemon had not been hurt.
The Argosí offence is the worst in the Canadian Football League and Lemon, though he has not been totally out of place, has not got into a rhythm.
Toronto, which plays host to the Saskatchewan Roughriders on Saturday in the first game of a home-and-home set between the clubs, has failed to score anything more than 17 points in its past five games. Four of those games have been losses.
Bell has thrown 10 passes this season, making five completions for 79 yards.
Bell would be backed up by Ken Dorsey, and Burlington native Danny Brannagan likely will be activated from the practice roster, unless Barker signs another quarterback.