Mullens (back) was designated for return from IR on Wednesday, Dane Mizutani of the St. Paul Pioneer Press reports.
Mullens will now have a 21-day window to practice with the team before needing to be added to the 53-man roster, although he could be added to it at anytime, including before Sunday's game against the Broncos. Once activated, he will likely serve as the backup to Joshua Dobbs.