Vikings first-round pick Christian Darrisaw visited Dr. William Meyers in Philadelphia this week for his second surgery of the year on a groin injury that's bothered him since before the draft.

Meyers, a noted specialist often sought by athletes dealing with core muscle injuries, performed what a league source called a minor procedure on Thursday morning. There's optimism Darrisaw can recover quickly and be ready for Week 1, the source said.

But coach Mike Zimmer wasn't as certain.

"That's what the doctors said, but I don't know," Zimmer said, when asked about Darrisaw being ready for the Sept. 12 season opener in Cincinnati. "They tell me one thing and it ends up being something else. I don't know."

Darrisaw has yet to participate in training camp beyond individual offensive line drills, after seeing some non-padded work in the team's mandatory minicamp. He had already been ruled out by Zimmer for Saturday's preseason opener against Denver at U.S. Bank Stadium — and Zimmer's frustration with the situation was palpable.

"It was taken care of in January," he said, referring to Darrisaw's predraft surgery. "We didn't expect this."

Offensive coordinator Klint Kubiak said that's meant more work for swing tackle Rashod Hill, who has been the team's starting left tackle throughout much of the offseason. Hill left practice after an injury Thursday, though he was able to stay on the field and watch the remainder of the Vikings' session with the Broncos.

Blake Brandel, one of the Vikings' sixth-round picks a year ago, stepped in for Hill with the first team at left tackle. It was a reminder of how tenuous the Vikings' tackle depth is, though Kubiak tried to strike an optimistic tone about Darrisaw.

"[Darrisaw] has been working his tail off," Kubiak said. "Cautious, taking it slow. When he's back, we'll take him. Otherwise, until then, getting a lot of good, extra work for Rashod."

Kubiak was asked how much time Darrisaw would need on the practice field to judge whether he's ready to start in the season opener against the Bengals.

"I wouldn't put a number on it," Kubiak said. "Any player coming off a major injury, they're all different. I'd say when he's been here, he's been really sharp and really dialed in. Mentally, I don't think it'll be a problem. We just got to get his physical reps and get his conditioning."