Antoine Griezmann said LaLiga champions Barcelona will improve as the season is long following Friday's shock loss to Athletic Bilbao.

Barca opened their title defence with a late 1-0 defeat away to Athletic at San Mames, where the holders succumbed to Aritz Aduriz's dramatic acrobatics.

Aduriz came off the bench and scored a stunning 89th-minute overhead kick to condemn Griezmann to a losing league debut for Barca.

"We have time," Griezmann, who arrived from Atletico Madrid, said after the match.

"The season is long and we have to work towards the next game.

"We have to work because that's the only way we'll improve."

Griezmann underwhelmed in his LaLiga bow for Barca – the €120million signing struggled to make an impact in the absence of injured captain Lionel Messi.

"We lacked what costs the most in football," the France star added.  "That last pass, that cross or that overlap."

Barca's defeat was compounded by an injury to veteran forward Luis Suarez, who was forced to leave the match in the first half.

Suarez suffered a muscle injury just after the half-hour mark, and Griezmann said: "Let's just see how he is and if he can play against [Real] Betis.

Barca – seeking a third consecutive LaLiga title – will travel to Real Betis on August 25.