Ernesto Valverde has admitted Barcelona may have to bolster their defence in the January transfer window if Samuel Umtiti continues to struggle with a knee injury.

Umtiti returned for the first time in almost a month against Atletico Madrid last weekend but still felt problems in his troublesome left knee and had to sit out Wednesday’s Champions League win over PSV Eindhoven.

Barca have confirmed the defender will now undergo treatment in Qatar as he attempts to find a solution to the problem, with Valverde conceding on Saturday that surgery is a possibility.

Valverde said buying some additional cover in January is also an option.

“From here until the January window, we have to go with our players and those in the B team, and then we will assess the situation,” Valverde said.

“We will see over the next month how Samu’s injury evolves. We have to be optimistic. We don’t really know if we will have to go to the market or not.

“There are various things to consider and when the winter market comes, we’ll see what we can do to solve it.”

Umtiti missed 10 matches before playing against Atletico, with 23-year-old Clement Lenglet, a summer signing from Sevilla, taking his place alongside Gerard Pique.

“We hope, and we are optimistic, that Samu can recover for the rest of the season,” Valverde added.

“On his decision to go to Qatar, there are several parties involved and we all have to agree, but the fundamental thing is the player. It’s his injury and he has to be convinced of things.”

Lenglet is expected to continue in defence when Barcelona host Villarreal in La Liga on Sunday, although Thomas Vermaelen has resumed training after shaking off a hamstring strain.

Arthur Melo is close to recovering from a groin problem and could also return but Rafinha and Luis Suarez are both out with knee injuries, along with Sergi Roberto, who has an injured hamstring.

Barca sit second in the table, one point behind Sevilla.