Michael McDonald was absent from last night's Doobie Brothers performance due to an unidentified illness.

After announcing before the show that McDonald would not be joining the band as scheduled, the Doobie Brothers addressed the issue early in their set. According to multiple firsthand reports, the group revealed that McDonald was “not feeling well” and that he was "recuperating and isolating at the moment." The band added that it expected the singer to rejoin the tour in a week or so.

Given the state of the world over the past 18 months, many people’s thoughts immediately turned to COVID-19. The Doobie Brothers did not say the virus was related to McDonald’s absence, but they did go out of their way to let the audience know that he, the band and their entire crew are all vaccinated.

The Doobie Brothers followed up last night's statement this morning by noting that "a member of their touring personnel" has tested positive for COVID-19 and that the group would be postponing its next four shows. They are currently scheduled to return to the road on Sept. 9 in Cuyahoga Falls, Ohio.

Originally announced in 2019 and scheduled for 2020, McDonald’s reunion trek with the Doobie Brothers was set to celebrate the band’s 50th anniversary. The tour was postponed a year due to the ongoing pandemic, but finally launched on Aug. 22.

Prior to hitting the road, McDonald admitted there was no way to predict whether things would go to plan.

“It’s a crapshoot, really, whether we’ll make it to the end of this or not, but I hope we do,” the singer confessed to the Associated Press. “The main thing I think is if we start to see that anything that we’re doing has a potential of being a super-spreader. I don’t think any of us are worried so much about getting sick ourselves. We’re all vaccinated. But if we test positive, that means all the people in our workplace are being exposed.”

Doobie Brothers Albums Ranked

They remain an intriguing dichotomy of a band.