ALAMEDA, Calif. -- The Oakland Raiders practiced Wednesday without a pair of key offensive players, running back Latavius Murray and center Rodney Hudson, as the team prepares to host the 6-2 Minnesota Vikings on Sunday. Standout receiver Amari Cooper, meanwhile, was on the field for the beginning of practice but went to the locker room and did not return with what the team called a quad issue.

After suffering a concussion Sunday, Latavius Murray can't play until he's cleared through the NFL's concussion protocol. AP Photo/Denis Poroy

Murray, who suffered a concussion in a 38-35 loss at Pittsburgh in Week 9, was in uniform but not participating in the 30-minute window during which media were allowed to watch practice Wednesday. Hudson, who suffered a sprained ankle in the fourth quarter against the Steelers, was not seen on the field at all during the media portion of the practice.

Murray, who is sixth in the NFL with 630 rushing yards, missed a game in December because of a concussion.

Raiders coach Jack Del Rio has been positive about Murray’s progress through the NFL’s concussion protocol. He must be fully cleared before he can play. Del Rio has been less expansive about Hudson, who signed a five-year, $44 million deal as a free agent in the offseason after spending the first four years of his career with Kansas City.

Backup Tony Bergstrom, replaced Hudson at Pittsburgh and was working with the first team Wednesday. Standout guard Gabe Jackson spent some time at center in the early portion of practice as a backup option.

Cooper spoke to the media earlier Wednesday and didn’t mention being injured, nor did he look to be in discomfort. He will be monitored during the week. The Raiders often keep players out of Wednesday drills as a precaution, which is always the case with veteran safety Charles Woodson.