Vermaelen out for six weeks with hamstring injury
The centre-back has damaged the femoral biceps of his right leg and is expected to be sidelined until the end of November, according to a club statement.
The news is a blow to Barca, who have already lost Samuel Umtiti to a knee injury that they reportedly fear could keep him out of action until the new year.
Vermaelen has only made three appearances this season but two of those have come in Umtiti's absence, most recently in the 1-1 LaLiga draw with Valencia at Mestalla.
The 32-year-old's injury is set to see him miss a daunting seven-match run that includes league games against Real Madrid and Atletico Madrid.
Barca host Sevilla on Saturday and Inter in the Champions League next Wednesday, before the Clasico at Camp Nou four days later.
Trips to Rayo Vallecano and Inter follow before a home game against Real Betis just prior to next month's international break.
MEDICAL REPORT: Thomas Vermaelen has a right hamstring injury. More details forthcoming. pic.twitter.com/mmACSOkstV
— FC Barcelona (@FCBarcelona) October 15, 2018