SANTA CLARA, Calif. — Barring a significant last-minute change, the San Francisco 49ers will start Mac Jones at quarterback for a second consecutive week Sunday against the Arizona Cardinals.

Starter Brock Purdy is listed as questionable for Sunday as he recovers from the toe injury that kept him out last week against the New Orleans Saints. And though Purdy was a limited participant in practice all three days this week and made what coach Kyle Shanahan called “a lot of progress” in his recovery, Shanahan wasn’t keen on Purdy’s chances of starting against Arizona.

“I think it’s highly unlikely that he will start,” Shanahan said Friday. “We’re just trying to see where he’s at to see if he can be a [No.] 2 or an emergency [No.] 3.”

Shanahan said whether Purdy is in uniform as a backup to Jones will depend on how Purdy feels over the next 48 hours. The Niners will see how Purdy is doing Saturday and then must make some roster decisions Saturday afternoon to determine whether Purdy can be the primary backup to Jones or whether they’ll need to again elevate practice squad quarterback Adrian Martinez to be Jones’ top backup.

According to Shanahan, the league rules state that if the Niners want Purdy to be the emergency No. 3 quarterback, the No. 2 quarterback (in this case Martinez) would have to be promoted to the active roster and could not just be a standard elevation who reverts to the practice squad Monday.

That decision could be made more difficult because of injuries on the 49ers’ offensive line. Rookie Connor Colby was expected to start at left guard in place of Ben Bartch (ankle), who landed on injured reserve this week, but Colby suffered a groin injury in Thursday’s practice.

Colby is listed as questionable against the Cardinals with Spencer Burford, another top backup offensive lineman, ruled out because of a knee injury that Shanahan said might require surgery.

All of that will play into the calculus of whether Purdy can be available against the Cardinals or whether he will be a pregame inactive, as he was last week. Shanahan indicated that the Niners still need to see certain things from Purdy over the next couple of days before they would have him as a backup because they don’t want to risk further injury.

Shanahan said Purdy will have his say in how it goes too, having demonstrated that he will be open with how Purdy is feeling in situations such as this.

“Brock pushes himself to go as hard as anyone I’ve been around, but he’s very levelheaded in terms of being realistic,” Shanahan said. “And he doesn’t just talk with his heart, he works with his heart but he talks with his mind and lets us really know what the chances are of it and if he can’t do it, he’ll let you know.”

For his part, Purdy said Thursday he wants to play but also doesn’t want to jeopardize any more games beyond this week.

“I want to play every game,” Purdy said. “I want to be out there. You only get 17 regular-season games, and every game matters, especially a divisional [game] going against the Cardinals. If you ask me, I’d love to, but I’m trying to be smart with my body here.”

Although Purdy participated in practice all week, there still have been plenty of signs that Jones was ready to start for a second straight week. Jones was first up in all the individual drills during the media viewing portions of practice and drew praise from teammates and coaches for how he played against the Saints.

In that game, Jones threw for 279 yards and three touchdowns as the 49ers improved to 2-0. That performance came after a sluggish start in which Jones said he was dealing with some nerves. Getting off to a better start is one of Jones’ top priorities this week, he said.

“I definitely watched it and learned from it and took all the coaching points and then have worked hard in practice to learn from the things I didn’t do as well and just get better at them,” Jones said. “I think the guys have done that and we’ve definitely moved on from that game. We’re just really focused on the Cardinals and stacking another good performance and carrying some good momentum into this week.”

In addition to Purdy and Colby, the Niners are listing wide receiver Jauan Jennings (ankle, shoulder) as questionable. Jennings did not practice this week after playing through the injuries against the Saints.

Rookie receiver Jordan Watkins joins Burford on the list of players the Niners have ruled out this week. Watkins suffered a calf injury in Thursday’s practice and is a candidate for injured reserve, according to Shanahan.