Marc Bartra has called on Barcelona to prove their strength when they take on Bayer Leverkusen without the injured Lionel Messi.

Messi was withdrawn early in the first half of Saturday's 2-1 La Liga win over Las Palmas with what was later confirmed as a knee ligament tear which will sideline him for up to two months.

Despite the blow of losing their talisman, Bartra is determined that the European champions will prove their mettle when Leverkusen visit Camp Nou on Tuesday for the second game of the Champions League group stage after they drew their opener 1-1 at Roma.

"It's bad news for us. Like it or not, Messi is our best player, the one who causes the most problems. I'm very sad for him," he told Barca TV.

"It's a major loss but now we have to become even stronger."

Messi became the first player to score five in a single Champions League game when Barcelona crushed Bundesliga outfit Leverkusen 7-1 in the knockout phase of the 2012-13 tournament, but Christoph Kramer believes it would be a mistake to forget the other stars at Luis Enrique's disposal.

"Of course any team would miss Messi, but Barcelona still have a world-class team without him," the midfielder told the official Bundesliga website.

"It's a game that we should look forward to. The team worked hard for a whole season [to play] this kind of match. We should enjoy the game and have fun.

"In football, anything is possible and we can definitely get something in Barcelona. We have to go into the game with confidence and be fully focused."

Claudio Bravo could return to action on Tuesday after he took part as normal in Sunday's training session, but Jordi Alba (neck) and Thomas Vermaelen (calf) remain major doubts.

Tin Jedvaj and Omer Toprak (both thigh) are still sidelined for Roger Schmidt's Leverkusen - who beat Werder Bremen 3-0 away from home at the weekend - while Roberto Hilbert (knee) is a doubt.

Leverkusen sit top of Group E following their 4-1 win over BATE in the opening round of fixtures but their record on Spanish soil is poor. They have won just three and lost 10 of their 15 visits in continental competition.

Barca have won the last five encounters between the sides, too, although Leverkusen did famously win 1-0 at Camp Nou in 1988 in the UEFA Cup quarter-final second leg - a tournament they went on to win.