There is a new showbiz axiom this year: If life gives you COVID, sometimes the show can go on.

At least, if you're the Doobie Brothers.

Co-founding guitarist-singer Tom Johnston had COVID early last year and the Doobies called off their shows in Las Vegas before the pandemic struck. However, on Tuesday, apparently some members of the Doobies entourage — they travel with a COVID compliance officer — tested positive. Keyboardist/singer Michael McDonald, who hasn't toured with the group for 26 years, was scratched in late afternoon for a sold-out concert at the Minnesota State Fair grandstand.

Part of the band's 50th anniversary tour, the performance went on anyway, as it has without McDonald for decades. (He was a member from 1975-82, then briefly again in 1987, 1992 and 1995-96.)

After the second song on Tuesday night, co-founder Patrick Simmons, a singer/guitarist, explained that McDonald was not feeling well.

"He's recuperating and isolating. We hope to have him back in a week or so," he said, adding that "it's what's happening these days.

"He's had his vaccine," Simmons said without ever mentioning COVID. "But the show must go on."

It did without any hitches, unless you consider trimming the set list by six tunes that the group had been performing with McDonald at the five previous gigs. So some of the 11,461 fans might have missed "What a Fool Believes," "Minute by Minute" and "You Belong to Me" that transformed the Doobies from classic rock to yacht rock.

The Doobies were eclectic before the term was commonplace. They mixed biker-bar rock with bluegrass, gospel, blues, country-rock and R&B before McDonald added his version of blue-eyed soul.

On Tuesday, the band showcased harmony vocals, harmonizing guitars and thick drums that it's long been known for. Without McDonald, the Doobies — Simmons, Johnston and guitarist John McFee, who joined in '79 —seemed neither especially spirited or dispirited at first. The performance — featuring material from 12 different Doobies albums including one due Oct. 1 — seemed professional.

Things started to turn around on the bluesy "Dark Eyed Cajun Woman" with a smoldering sax solo by Marc Russo, one of five sidemen to the core Doobies. But it took the hits to bring the crowd to its feet as Simmons assumed McDonald's lead vocals on 1976's "Takin' It to the Streets."

Johnston had plenty of sass in his voice on "Eyes of Silver," which featured Russo throwing in Princely sax licks. The Doobies began cooking on deep tracks "Neal's Fandango" and "Without You," a hard boogie with Johnston, Simmons and McFee dancing in unison ZZ Top-style. Then it was time for the hard-charging home stretch of hits: "Jesus Is Just Alright," which suggested the Doobies are a tight jam band; the short and punchy "Rockin' Down the Highway"; the propulsive "Long Train Runnin' "; and the buoyant "China Grove." The encore juxtaposed the fiddle-spiked "Black Water" with the joyous singalong "Listen to the Music."

If McDonald had participated, he would have added different flavors and textures for the Rock Hall of Famers. When Simmons introduced the band, he pointed to his right and announced, "This [empty] space is Mike McDonald." The comment was neither snide nor comical. With or without him, they're still the Doobie Brothers.