FC Barcelona have confirmed an injury to their striker Robert Lewandowski.

According to SPORT, it is feared that the Pole could miss more than just Sunday's La Liga fixture against Granada and possibly El Clasico later this month as well.

Lewandowski left Barca's 1-0 Wednesday night win over Porto in the Champions League early.

Moments before his exit, the referee of the fixture didn't call a foul when he received a knock to the ankle, which caused the veteran to writhe on the turf in pain.

Lewandowski had to be hooked by head coach Xavi Hernandez who introduced Ferran Torres up front as a replacement.

Torres was the hero of the evening for scoring the only goal of the game approaching half time, and making sure that the Catalans kept their 100% record in Europe's elite competition intact.

Losing Lewandowski and Lamine Yamal prematurely - in addition to Gavi when he was red-carded - were sour notes for the visitors however, and Xavi was probed on his number 9's situation post-match.

The manager explained that the player had received a "very strong blow" to his ankle and couldn't continue. And on Thursday afternoon in Catalonia, Barca confirmed a knock that will keep him sidelined.

"Tests carried out this morning have revealed that Robert Lewandowski has a left ankle sprain. He is out and his recovery will determine his availability," a statement published on Twitter read.

As is standard practice, Barca haven't included any sort of timeframe for when their top scorer might be back in action.

While it was originally thought that Lewandowski would only miss Sunday's meeting with Granada and then be fit after resting over the international break, SPORT reports that he could be out "for more than a month" which would scrap any potential involvement in El Clasico.

Barca face their eternal rivals Real Madrid, in the latest installment of the world's biggest derby, on October 28 at the Montjuic Stadium.

If Lewandowski is really ruled out for the quoted timeframe, he will miss important La Liga matches against Granada, Athletic Club, Madrid, and Real Sociedad at a minimum.

Following this logic, Xavi also won't be able to count on last year's winner of the Pichichi in the Champions League when the Blaugrana face Shakhtar Donetsk on October 25 - and possibly the return away fixture on November 7 as well.

Today's news contributes to a growing headache for Xavi and his staff, who have lost midfielders Frenkie de Jong and Pedri to injuries too.

That's now three star players which might not be ready to lock horns with Los Blancos, and a lack of out-and-out target men means Ferran Torres will have to lead the line from now until Lewandowski's return.