Barcelona coach Hansi Flick said his team must learn quickly from Monday's 3-0 defeat to AS Monaco as they prepare to kick off the new LaLiga season against Valencia at Mestalla on Saturday.

Lamine Camara, Breel Embolo and Christian Mawissa all scored in the second half as Monaco became the first team to beat Barça in the annual Joan Gamper Trophy match since Sampdoria in 2012.

"Now is the right time [to lose], not when the season starts," Flick told Barça One. "We have to learn from this match, analyse everything, show the players and make it better on Saturday against Valencia."

Barça's preseason has been hampered by international tournaments and injuries, with European Championship winners Lamine Yamal and Ferran Torres coming off the bench against Monaco to make their first appearances of preseason.

Olympic gold medial winners Eric García, Pau Cubarsí and Fermín López are yet to feature, though, while Ronald Araújo, Gavi, Pedri and Frenkie de Jong are all injured ahead of the weekend's curtain-raiser against Valencia.

Despite that, Barça had chances to take the lead against the Ligue 1 side, with Pau Victor, who scored a brace in the win against Real Madrid last week, guilty of missing the best opening.

"We could have gone 1-0 up and maybe it's different," Flick added. "When you're a team like Barça, you have to score this goal. It's very important to score at the right time.

"We didn't play with our normal speed or normal combinations. We lost a lot of balls. Monaco got better and better in the first half so we wanted to change something in the second half. And then it was an individual mistake, they scored the 1-0.

"But at the end, it is preseason. I know the team can play much better than today. We have five days more now and will prepare them well for the next match against Valencia."

Sergi Roberto will not be involved against Valencia after it was confirmed this week that he will leave the club following the expiry of his contract in June.

On Tuesday, the Barça squad attended a farewell event for the former club captain, with ex-coach Xavi Hernández, Gerard Pique and Carles Puyol also among those present in the audience.

"In recent years I have seen legends and teammates leave and today is my turn," Roberto, who at times struggled to hold back the tears, said.

"At 14, I fulfilled a dream wearing a Barça shirt for the first time and I have enjoyed every day since as if it was the last.

"Who would have told me I would go on to play 373 times for the club of my life? And that I would become the club captain, following [Lionel] Messi, [Sergio] Busquets, Xavi and Co.?

"I would like to have said goodbye to fans on the pitch, but I want them to know I am eternally grateful for their support and will always carry them in my heart.

"And I wish my teammates the best in the future -- you have another supporter here celebrating every win."

Roberto had been training at Barça's facilities this summer and talks had taken place over a new deal, but his 18-year-association with the club has now come to an end.

Sources have told ESPN there is interest from clubs in Spain, Italy, the Netherlands and England in signing the midfielder, who scored the sixth goal in the famous 6-1 comeback win against Paris Saint-Germain in 2017.