The Associated Press reports that Sambora will not be playing with Bon Jovi during the current leg of the band's Because We Can tour, including Sunday's concert in St. Paul.
The band announced that all shows would go on as scheduled, but "personal issues" are keeping Sambora out of the lineup.
TMZ reports that Sambora first missed Tuesday night's Bon Jovi concert in Calgary.
According to the site, Jon Bon Jovi told the crowd, "I had two choices: Pack up and go home or give you everything I got ... Richie Sambora won't be performing for a while. If there's ever a night I need you, it's tonight, Calgary!"
Sambora on Tuesday, meanwhile, noted on Twitter just hours before the announcement that that he was "Watching more of the 'Every Road Leads Home To You' cover videos," referring to a fan contest connected with a promotion of a song on his solo album, "Aftermath of the Lowdown."
The guitarist followed up with a Tweet Wednesday evening, saying "I'm well," noting, he "had to stay in LA to take care of a personal matter."
While several outlets including Entertainment Weekly and The AP noted the 53-year-old Sambora's past stints in rehab, sources "directly connected" to Bon Jovi tell TMZ that substance abuse is not the issue for missing the concerts, and instead it's due to an escalating rift between Sambora and Jon Bon Jovi -- described by one source as "a classic Jagger/Richards blow-up."