Dallas Cowboys backup running back Lance Dunbar has been a revelation this summer after a relatively disappointing rookie season in 2012.

After gaining clear separation from fifth-round draft pick Joseph Randle though the favorite for the No. 2 tailback job received bad news on Monday.

Dunbar is expected to miss roughly three or four weeks with a sprained left foot that required a walking boot according to Nick Eatman of the Cowboys' official website.

The injury appeared to occur at the end of a 43-yard catch-and-run that resulted in a fumble when Dunbar landed awkwardly after having his legs tripped up.