MUNICH -- The New England Patriots placed running back TreVeyon Henderson on injured reserve Saturday, eight days after Henderson said he recently experienced "an unexpected and unusual medical emergency involving a series of unexplained neurological symptoms."

Henderson had already been ruled out for Sunday's game against the Detroit Lions at FC Bayern Munich Arena (9:30 a.m. ET, Fox) earlier in the week. He now will miss at least the next four games.

Henderson has said that tests have "come back positive and reassuring," and in a social media post said, "the cause of this remains unknown and unexplainable."

The Patriots entered the week with just two healthy running backs -- Corey Kiner and Lan Larison -- as starter Rhamondre Stevenson was managing a knee tendon issue sustained in last Sunday's loss to the Packers.

Stevenson was a limited participant in the Patriots' two practices in Munich, and coach Mike Vrabel said Friday he was feeling "pretty good" when asked to gauge Stevenson's potential availability for the game at that point. Vrabel said the same thing about wide receiver A.J. Brown, who has missed the last two games with a knee flare-up.

A potential tip-off that Stevenson could be active for Sunday's game against the Lions came when Saturday's deadline to elevate players from the practice squad passed, and the Patriots didn't elevate a running back. Going into a game with just two running backs would be outside the norm, as most teams have at least three.

In other roster moves, the Patriots activated center/guard Greg Van Roten and fullback Reggie Gilliam to the active roster from injured reserve, and elevated center/guard Andrew Rupcich from the practice squad for Sunday's game.