The diagnosis, which would rule Gallup out for the rest of the season, is pending further tests.
Gallup’s left knee appeared to buckle as he turned to catch a 21-yard touchdown pass from Dak Prescott in the second quarter. He clutched the knee after the officials ruled the catch was good. He was able to walk off the field but went immediately to the medical tent for further evaluation.
Gallup is scheduled to be an unrestricted free agent when the season ends.
He suffered a calf injury in the season-opening loss to the Tampa Bay Buccaneers and missed seven games. He had 32 receptions for 409 yards and a touchdown entering Sunday and caught three passes for 36 yards and a touchdown against Arizona.
With Gallup out, the Cowboys moved Cedrick Wilson into the No. 3-receiver role opposite Amari Cooper and CeeDee Lamb. The Cowboys managed to get along well without Gallup early in the season, but they struggled Sunday vs. Arizona.
The loss dropped Dallas to the No. 4 seed in the NFC with one week left in the regular season.