Arsenal manager Arsene Wenger will choose from a pool of experienced players to lead the side during Mertesacker's absence.
"Per is a very respected figure in the dressing room, is loved as well and is also a very demanding figure," Wenger told Arsenal Player.
"I think it is absolutely natural to be (him).
"(In his absence) that's where it will be taken by the assistants.
"One of them will be (Laurent) Koscielny, also (Santi) Cazorla - the experienced players - (Petr) Cech maybe.
"We will have a group of people that will take care of the energy levels and the problems of the team.
"That will be down a lot to the experienced players."
Arsenal needed to appoint a new captain following Mikel Arteta's departure this summer.
The Spaniard's injury problems over the last two seasons have seen several players fill in as temporary captain.
Mertesacker, who joined Arsenal from Werder Bremen in 2011, captained the side on occasions last season before he was dropped as Wenger preferred to partner Gabriel and Koscielny at the heart of his defence.
The permanent appointment of the World Cup winner is also something of a surprise after Wenger said last month that he does not expect to have Mertesacker available again until the turn of the new year.
The 31-year-old suffered a knee injury in a pre-season friendly with Lens and could be sidelined for up to five months.
Source : PA