Mullen will undergo toe surgery, and head coach John Harbaugh expects him to miss the season, Jeff Zrebiec of The Athletic reports.
Mullen was already set to miss the first four games of the season after being placed on the reserve/non-football injury list Friday. Now it appears his absence will likely extend beyond that. The 25-year-old was expected to compete for a depth role in the secondary after being claimed off waivers from the Cowboys in January.