Willis will be evaluated by the same specialist who has been treating Bengals receiver A.J. Green’s toe ligament problem.
The seven-time Pro Bowl selection has 34 combined tackles, three passes defended and one interception this season. He only missed six games during the first seven seasons of his career since being a first-round pick by the 49ers in 2007.
Rookie Chris Borland replaced Willis and had two tackles. The 49ers' depth at linebacker is being put to the test. NaVorro Bowman is reportedly still a few weeks away from returning after tearing his left ACL and MCL during last season's NFC Championship Game. Aldon Smith is serving a nine-game suspension for multiple off-field issues.
San Francisco has the No. 2 ranked defense in the NFL, allowing only 287.2 yards per game.
Following a 1-2 start to the season, San Francisco has won three straight games. The 49ers are 4-2 and play the Broncos in Denver on Sunday at 8:30 p.m.
- Paul Palladino