All eight Vikings players who missed Sunday's practice because of presumptive positive COVID-19 tests were back on Monday, as the NFL said it had gotten to the root of the problem that produced 77 false positive tests among players, coaches and team staffers over the weekend.

BioReference Laboratories, the company handling the NFL's coronavirus testing program, said in a Monday statement that an investigation indicated the positive results were "most likely" erroneous and blamed them on contamination in a New Jersey laboratory.

"I do believe the problem has been corrected," Dr. Allen Sills, the NFL's chief medical officer, said in a conference call Monday.

The mixup took eight Vikings players and one coach off the field for Sunday's practice. Linebacker Eric Kendricks, defensive ends Jalyn Holmes and Kenny Willekes, fullback C.J. Ham, wide receivers Dillon Mitchell and Alexander Hollins, tight end Nakia Griffin-Stewart and tackle Ezra Cleveland were absent, as was assistant special teams coach Ryan Ficken.

"The guys didn't blink an eye, Coach Zim didn't blink an eye, [infection control officer Eric Sugarman] did a great job of coming in and expressing to us what was going on," co-defensive coordinator Andre Patterson said in a videoconference Monday. "We followed the protocol. There was no anxiety. There was nobody worried or walking around, trying to see who was here, who wasn't here. The guys did an outstanding job, and I think the coaching staff handled it good, too. That was probably a good experience for all of us."

If the same thing happens on a game day, Patterson said, "hopefully we deal with it like we did yesterday.

"They're not going to cancel the game. Whoever you play is not going to feel sorry for you. You've just got to go deal with it, and you go play. You have confidence in the guys that have got to go out there and play. I look at it no different as somebody getting hurt the day before the game, or somebody woke up Sunday morning sick — which we've had happen before. You go play."

Coach Mike Zimmer did not speak to reporters on Monday.

Eleven NFL teams, including the Jets, Browns Bears and Lions, were affected by the erroneous test results. Former Vikings offensive coordinator Kevin Stefanski, now the Browns' head coach, told reporters in Cleveland he was one of the team's false positive tests over the weekend.

"It wasn't fun to have that phone call very early in the morning and not get the news it was a potential error until later,'' he said.

The league released test results for Aug. 12-20, during which players were tested daily. The NFL said it administered 23,260 tests to players and there were zero positives.

Vikings back to normal practice

The Vikings were back on their outdoor fields for Monday's practice, after Sunday's false positive tests left them feeling shorthanded enough for Zimmer to move practice inside because of the heat. Here are some observations from Monday's practice:

• Defensive end Danielle Hunter, who hasn't practiced since Aug. 16 because of what Zimmer has described as a "tweak," remained out on Monday. Punter Britton Colquitt, who hasn't been seen punting in practice recently, also did not participate.

• Wide receiver Justin Jefferson got some work with the Vikings' first-team offense, posting a nice catch-and-run on a screen from Kirk Cousins. Jefferson also spent the last period of practice getting advice from Adam Thielen while the Vikings' special teams units were on the field.

• There were some rough moments for cornerback Holton Hill in 11-on-11 work. He dropped an interception and got beat by Thielen in the red zone before Cousins hit Thielen on a fade route at the end of practice.