Starting right tackle La'el Collins was walking with a noticeable limp and had his left ankle heavily taped at Thursday's practice, according to ESPN.
The Cowboys already are missing two of their top interior linemen. Center Travis Frederick is out indefinitely while receiving treatment for Guillain-Barre syndrome -- an auto-immune disease -- and Pro Bowl guard Zack Martin is sidelined with a hyperextended knee.
Collins started all 16 games at right tackle for Dallas in 2017. He was shifted from guard to tackle prior to last season and signed a two-year, $15.4 million extension.
An undrafted free agent out of LSU in 2015 whose stock plunged after he was listed as a person of interest in a murder investigation in Louisiana, Collins started 11 games at left guard as a rookie and three during the 2016 season before landing on injured reserve with a toe injury.
Frederick announced via Twitter on Wednesday that he was receiving treatment for Guillain-Barre syndrome and reported improvement "from an overall strength perspective."
Martin was hurt in a preseason game against the Cincinnati Bengals over the weekend, but he is targeting a return in the regular-season opener versus the Carolina Panthers on Sept. 9.