Barcelona have received a double injury blow with confirmation that Gavi and Fermín López are both set for a spell on the sidelines.
Gavi requires a minor operation to deal with a meniscus problem in his knee.
Barça have not revealed how long the midfielder will be out, but a source told ESPN he is expected to be out until at least November.
Fermín, meanwhile, will be out of action for around three weeks after injuring a muscle in Sunday's 3-0 win over Getafe.
Gavi, who returned from an ACL injury in the same knee last season, has not featured since August.
Barça had hoped surgery would be avoidable, but that has not proven the case in the end.
"Gavi underwent intense sporting stress tests after finishing his conservation course of treatment for the radial injury to the internal meniscus in his right knee," a statement said.
"The conclusion is that in order to guarantee the best possible recovery and return to competitive action, this Tuesday Gavi will undergo an arthroscopic examination by Dr. Joan Carles Monllau, under the supervision of the club's staff."
- Source: Rashford benched over 2 mins late arrival
- Ferran Torres bags brace as Barcelona ease past Getafe
- Flick on Yamal's Ballon d'Or hopes: 'One day'
Fermín will be back sooner, but is still set to miss several games, starting with Real Oviedo on Thursday, Real Sociedad on Sunday and the Champions League game against Paris Saint-Germain next week.
"Fermín has an iliopsoas muscle injury in his left leg," Barça's statement added. "He will be out of action for around three weeks."
Elsewhere, Alejando Balde is nearing a return from a hamstring problem and Lamine Yamal is also pushing to return to action after missing the last three games.