The 21-day window is part of the COVID-19 protocols enacted by the Big Ten. It begins from the time of the first positive test. If his first test was taken Saturday, Mertz - who put together a flawless performance in Wisconsin's season opener against Illinois - could be eligible to return to the team Nov. 14.
Badgers' upcoming schedule
Mertz entered the season second on Wisconsin's depth chart, but he was promoted when starter Jack Coan suffered a foot injury in practice. Third-stringer Chase Wolf also produced a positive test, but he's awaiting results on the second test, a source told Jeff Potrykus of the Milwaukee Journal Sentinel.
Mertz, the most heralded quarterback recruit in Wisconsin history, completed 20 of 21 passes and threw five touchdowns against Illinois.