Despite winning all three games in LaLiga so far, Hansi Flick believes Barcelona still have room to improve ahead of their clash with Rayo Valladolid.

With rivals Real Madrid struggling to fit new signing Kylian Mbappe into their stellar squad, and winning only one game so far, Barca have opened up a lead at the top of the league standings on nine points, two ahead of second-placed Villarreal and three from Celta Vigo in third.

"It's going to be a long season, and I'm not focused on the opponents. I'm focused on Barca, we've done well in the first three games and hopefully tomorrow we'll be victorious," Flick told a press conference on Friday.

"The players are fit and rested, they are training really well, and I'm pleased. We believe in our strength and in our idea of the game.

"Of course, there are many things we need to improve, like being focused from the start of the matches and not wait 10 minutes to get going. To be confident from minute one, that's what I expect from the players.

"It sounds like something basic, but it's part of the hard core of our idea of the game. The quality of this team is sky-high, fantastic."

Barcelona had to fight back to win after conceding first-half goals at Valencia and Rayo Vallecano, and needed a late Robert Lewandowski winner to break the deadlock at home against Athletic Bilbao.

Flick said he was delighted with the strength of character in the team.

"We have a special atmosphere and a very good mentality. They are very professional players with a great attitude. They are acting as one. The attitude, the mentality, the teamwork... I love it. This is the only way to win, in unison," Flick said.