The 5-foot-10 Grimes was signed off the Texans' practice squad by the New York Jets in September. The Jets waived him on Tuesday, and the Texans picked him up with Ben Tate's status uncertain for Sunday's game against Buffalo (3-4) because of a hamstring injury.
Grimes was an undrafted free agent out of William & Mary. He left as the school's career leader with 4,541 yards rushing, 7,955 all-purpose yards, 2,289 kickoff return yards and 936 rushing attempts. Grimes also earned 11 all-conference honors during his career, the most in Colonial Athletic Association history.
The 6-3 Alexander made five tackles in six games for the Texans this season.