The crack is in a column in the north side of the building, near the site of Friday's collapse, which sent a large street-level glass canopy crashing down onto the two underground parking levels.
Approximately 100 columns support the building, and about 30 are in the area of the garage collapse, said Hackensack construction official Joseph Mellone.
Engineers were still determining if the crack in the column existed before the collapse, Mellone said, adding that the crack appeared repairable.
Meanwhile, residents who were evacuated Friday and have been staying with friends or in nearby hotels since then will be allowed back into their apartments Wednesday to collect personal belongings, Lt. Stephen Lindner, a city fire department spokesman, said Monday.
It was not clear when they would be allowed to move back into the 18-story Prospect Towers.
"I don't have an answer for that yet," Mellone said. "It's still too early in the game. Right now we're trying to gain control of the building."
The collapse initially was feared to have trapped at least one person inside a car, but rescuers later determined that no one was in the garage. Officials said Monday that rescuers had about a dozen cars left to search, but everyone in both buildings that use the garage had been accounted for.
Another partial collapse occurred Saturday afternoon, but no injuries were reported, though power was lost in the building. Crews were removed as a precaution and the cleanup work was temporarily suspended.
The south side of the underground garage was left intact and didn't appear in danger of collapsing, Mellone said. Workers were busy continuing to shore up the walls of the parking garage Monday.
The cause of the collapse is unknown, city officials said.
Engineers retained by the city and by the building's owner, Equity Residential Properties of Chicago, have been examining the wreckage for the last several days.
Hackensack city manager Steve LoIacono said officials were checking into reports that the building's owner had been notified in the spring by its engineering firm that a leak in the parking garage was making the structure unsafe.
LoIacono added that the city was not aware of problems at the building, but the owner would not be required to file for a permit with the city to do investigatory work such as digging. Numerous residents said Friday that workers had been digging in the garage area beginning several months ago.
A spokesman for Equity did not immediately return a phone message Monday.