SANTA CLARA — The 49ers’ quarterback situation? Call it a practice-time decision.

They are waiting to see how today’s practice goes and to what extent Jimmy Garoppolo participates, after missing the previous two days because of a calf injury.

“He wanted to get out there, but it was just too painful Wednesday and Thursday. Jimmy’s been living in the training room, trying to get out there,” general manager John Lynch said on KNBR 680-AM. “Today is critical. If it’s not today, then we go with Trey.”

“Jimmy told me he wants to give it a go tomorrow, so we’ll see him out on the practice field tomorrow,” coach Kyle Shanahan said on KNBR after Thursday’s practice. “If he looks good, then he’ll have a shot. If he can’t, then we’ll shut him down.”

Rookie Trey Lance, indeed, has prepared as if Sunday will be his first career start when the 49ers (2-2) visit the Arizona Cardinals (4-0).

Lance passed for 157 yards and two touchdowns, and also ran for 41 yards, in second-half relief of Garoppolo in Sunday’s loss to Seattle.

“Trey’s got a quick mind, progresses quickly out there, and sees things well,” Lynch said. “Having said that, there’s a lot he hasn’t seen yet. The great thing there is he has incredible feet, can move around and can make things happen.

“He got better throughout the game and we’ve seen that out here at practice. With reps, a guy like him gets better. He’s so talented. He has a quick, sharp mind. There’s a lot of encouraging things. But we’re not trying to be encouraged. We’re trying to win. And we’ve got a tough, tough job ahead of us, because the Cardinals are playing really good football, it’s a super-talented team.”

Garoppolo sustained a right-calf contusion on Sunday’s opening touchdown drive and did not return after halftime. Lynch noted that because the issue is with Garoppolo’s right leg, it hinders his ability to push off on throws. He’s missed 23 starts because of injury since 2018.

Teammates have walked the fine line of both supporting Garoppolo’s recovery efforts and Lance’s potential starting debut.

Wide receiver Trent Sherfield, who played his previous three years with the Cardinals, talked Thursday about Lance’s strong work ethic and how that’s set him up for a promising career.

“He’s here late. He’s in the film room late. He’s doing all the right things to put himself in position,” Sherfield said. “He’s 21 years old, and the guy can play football.

“He’s going to be really, really good. His ceiling is very, very high. You guys got a glimpse of that last week.”

Left tackle Trent Williams said of Lance: “He has a confident aura around him, where you believe in him the more you’re around him.”

Lynch didn’t take those two endorsements lightly, saying that Williams and Sherfield are two veterans who command respect when they speak.

“When they speak, they mean it, it’s authentic. I would agree with them,” Lynch said. “They’re speaking their mind and truth that they have a lot of belief in Trey, we all do.”

Garoppolo is not the only injury concern, of course, on a franchise jinked by poor health for years.

Tight end George Kittle has not practiced this week but he, too, could test out a calf injury today. Only cornerback K’Waun Williams (calf) is ruled out at this point for Sunday’s game, although defensive tackle D.J. Jones’ absence from Thursday’s practice with a knee injury is a new concern.

The 49ers are quite familiar with Arizona’s stadium, having played their final three home games last season after being exiled from Santa Clara County’s health code, and although they lost all three, they did win there when the Cardinals hosted them in December.

With Arizona the only unbeaten team left in the NFL, the 49ers are expecting a big-time atmosphere, and that is more adjustment Lance would have to make if he starts or plays.

“We’re heading into a place, 4-0, that stadium can get loud,” Lynch added. “I don’t think North Dakota State played in front of 60,000 people or 70,000 people. The nice thing about Trey is they did play a very much pro-style offense. It’s been talked about how he only threw it 318 times in college, so just the more reps you get, the better you get.

“He’s taken to our offense well,” Lynch added. “Every rep he’s going to get better. For every player, the speed, and the collective speed, your margin for error is reduced 10-fold, 20-fold. You have to be on point, make quick decisions and can’t be late. All those things he’s going to learn and already has. Playing is going to be really critical for him.”