The running back suffered a pulled left hamstring in practice Tuesday and is expected to be out four-to-six weeks.
While not ideal, Kackert's injury wasn't related to the broken left ankle he suffered last year that forced him to retire prior to the start of the season.
Kackert, 28, ended his retirement last month to join Toronto's practice roster in hopes of returning to the starting lineup.
Kackert broke his ankle prior to the 2013 East Division final and was forced to retire the first day of training camp because the injury hadn't healed sufficiently.
Kackert remained with the Argos as their strength-and-conditioning coach.
The five-foot-eight 206-pound Kackert was a big-play running back during his three seasons with Toronto, rushing for 1,467 yards and 12 TDs on 228 carries (6.4-yard yard average). He added 50 catches for 454 yards and two touchdowns.
He was the 2012 Grey Cup MVP after rushing for 133 yards on 20 carries in Toronto's 35-22 win over the Calgary Stampeders at Rogers Centre.
Note to readers: This is a corrected story. A previous version said Kackert suffered the injury Wednesday.