NFL and NFLPA officials are looking at MetLife Stadium turf Wednesday, a source told Jonathan Jones of CBS Sports.
San Francisco plays the New York Giants on the same field in Week 3.
Bosa and Thomas suffered ACL tears and won't return this season, while Garoppolo is considered day-to-day with an ankle injury. Mostert, who's battling a knee ailment, reportedly isn't expected to play against the Giants.
The NFL addressed the issue Monday.
"The independent field inspector determined on Sept. 12 that the field was in compliance with all applicable NFL policies, including the Mandatory Practices for Artificial Surfaces," the league said, according to NFL Network's Ian Rapoport. "In addition, within 72 hours of each home game, clubs must certify that their fields are in compliance with applicable NFL policy, and that occurred in this instance."