Watkins has been dealing a foot injury that forced him to sit out last week's 26-14 victory over the Arizona Cardinals. An MRI exam taken in the week leading up to the Arizona game did not reveal any structural damage to the foot.
On Thursday, Watkins was able to practice on a limited basis but he did not take the field Friday or Saturday. That's an ominous sign that he will not face his former team on Monday night.
Kansas City and Los Angeles will enter Monday night's high-octane matchup with identical 9-1 records.
Watkins has 39 receptions -- matching his season total with the Rams in 2017 -- for 515 yards and three touchdowns for the Chiefs. He had a team-high eight receiving scores for Los Angeles a year ago.
Despite a disappointing season with the Rams, Kansas City signed Watkins to a three-year, $48 million contract in the offseason.
The 25-year-old Watkins, a former No. 4 overall pick of Buffalo in the 2014 NFL Draft, missed the first eight games of the 2016 season due to a broken bone in his foot.
The 6-foot-1, 211-pound Watkins had an outstanding rookie campaign will the Bills, posting a career-best 65 receptions for 982 yards and six touchdowns. He followed that up by going over 1,000 yards (1,047) the following season and posted a career-high nine touchdown catches.