49ers' Vernon Davis, backup Vance McDonald questionable for Sunday (w/video)

SANTA CLARA - San Francisco 49ers tight end Vernon Davis did some light running and caught passes from a machine Friday and remains questionable for Sunday’s game at the Arizona Cardinals.

Davis, recovering from an ankle injury suffered during the 49ers’ loss to the Chicago Bears last weekend, said he would be ready to play if he’s given the green light, despite missing the week of practice.

Backup tight end Vance McDonald, recovering from a knee injury also suffered in the loss, could also return to action. He’s listed as questionable.

“I’m always optimistic in all phases of my life,” McDonald said. “If it were up to me, I’m going. We’re being patient with it.”

Derek Carrier and Kyle Nelson, who is the team’s long snapper, are the only healthy tight ends available. Carrier, a second-year player, caught his first three career passes during the fourth quarter against the Bears.

“We’re confident in Derek,” 49ers coach Jim Harbaugh said. “He played well the other night. He’s a good player.”

49ers offensive coordinator Greg Roman said Carrier has a lot of upside and that he’s been involved in practice since Day 1 with quarterback Colin Kaepernick.

“There’s definitely things he needs to work on, but he’s done a nice job,” Roman said. “He has a good feel for the passing game and has really improved his blocking in this preseason. That was the number one thing that I’ve been most pleased with.”

Nelson, who scored a pair of touchdowns in the preseason, would most likely be used only in an emergency, though Harbaugh acknowledged he was encouraged by Nelson’s pass-catching ability.

“Anything is possible,” Harbaugh said. “You always like to have those options and have your opponent think that there could be any option available.”

McDonald and center Daniel Kilgore serve as Nelson’s backup at long snapper.

Meanwhile, Davis said he felt fine after Friday’s practice.

“It feels great right now,” he said. “I’m just going to take it slow and leave it to the trainers and coaches.”

Davis familiarized himself with the game plan, not just in case he can play but also if he could provide some input for Carrier.

“I’ve been through a lot,” Davis said. “It’s like anything. You get injured, you come back, and you make the transition.”