Wisconsin quarterback Graham Mertz had his COVID-19 positive test confirmed and will be out a minimum of 21 days, a source has confirmed to ESPN.

Mertz, who starred for Wisconsin on Friday in its season-opening win over Illinois, had an antigen test come back positive for the coronavirus over the weekend. He had a polymerase chain reaction (PCR) test that confirmed the result Monday. Big Ten policy requires any player who tests positive for COVID-19 to miss at least 21 days and undergo cardiac screening before being cleared to return.

CBS Sports first reported the confirmation of Mertz's test.

Wisconsin could be down to its fourth-string quarterback for Saturday's game at Nebraska after third-stringer Chase Wolf also tested positive, per sources, confirmed a Monday night report by the Milwaukee Journal Sentinel. If Wolf's positive test is confirmed, he also will miss a minimum of 21 days before returning to action.

Jack Coan, the Badgers' projected starter this season, suffered a foot injury in preseason practice and underwent surgery Oct. 6. Coan, who started 18 games the past two seasons, is out indefinitely. Redshirt junior Danny Vanden Boom is expected to make his first start against Nebraska if Wolf is also out.

Vanden Boom appeared in three games in 2018, completing the only pass he attempted for a 3-yard touchdown. After Nebraska, Wisconsin hosts Purdue before visiting No. 13 Michigan.

Wisconsin coach Paul Chryst said Monday that he could not comment on any player's status relating to COVID-19 testing or results. Chryst said he was confident that the Nebraska game could still be played. If a team's positivity rate -- the number of positive tests divided by total number of tests administered, based on a seven-day rolling average -- exceeds 5%, it would not be allowed to play and the game would be declared a no contest.

Chryst said he has no issue with the Big Ten's 21-day policy for players who test positive, which is more stringent than those of other leagues.

"The No. 1 concern for the league, and I appreciate this, was how do we best keep everyone as safe as possible regarding the virus, and then how do you manage the impacts of it when someone has it," Chryst said Monday. "Admittedly, they told us it was more conservative, and if that helps one person, then that's a good thing for us. We've known that there was a lot of work that went through this. For us to play, if that is something that's in the best interest of everyone involved, then I completely support it."

In a statement issued Sunday night, Wisconsin said it "will not be releasing COVID-related testing information regarding any individual student-athlete, due to medical privacy."

The statement noted that no player who participated in Friday's game tested positive before the game or reported any symptoms.

"Wisconsin Athletics continues to conduct daily antigen testing for the student-athletes, coaches and selected support staff associated with the Badger football program," the statement read. "Individuals who receive a negative antigen test result continue to participate in team activities. Individuals who receive a presumptive positive antigen test result are removed from team activities and are required to take a PCR test to confirm positivity."

Mertz, a redshirt freshman, was nearly flawless Friday in a 45-7 win over Illinois. He completed 20 of 21 passes for 248 yards and five touchdowns. He set team records for single-game completion percentage (95.2) and touchdown passes. Mertz completed his first 17 pass attempts, matching a team record for consecutive completions.

A native of Overland Park, Kansas, Mertz is considered the top quarterback recruit in Wisconsin history. ESPN rated him as the top pocket passer and No. 21 overall player in the 2019 recruiting class.