Mick Jones of Foreigner has missed the band's big gig with Journey at the Hollywood Bowl in LA, sparking worry among fans.
A near-capacity crowd watched frontman Kelly Hansen, a replacement for the the original singer Lou Gramm, and watched the band play Cold as Ice, Jukebox Hero, Waiting For a Girl Like You and I Want To Know What Love Is, but Jones was a no-show.
It has emerged that illness has prevented him from performing for over a month.
The rocker's management and agent have not commented on what ails him, but insist he is 'recovering well and we expect him to be back with us soon.'
The Journey/Foreigner tour continues in northern California with a show in Fresno on Wednesday.
Fan message boards suggest Jones hasn't been performing with the band he founded since 20 August 2011.