Lionel Messi's decision to stay has given Barcelona a huge boost ahead of the new season, says new coach Ronald Koeman.

After initially telling Barca he wished to leave after a trophyless campaign, and amid frustration with the Camp Nou board, Messi performed a U-turn and elected to stay with the Catalan giants.

Messi's contract expires next year, with Barca having been desperate to keep hold of their superstar as they look to overhaul the squad under Koeman, who replaced Quique Setien last month.

Last season's runners-up kick off their LaLiga campaign against Villarreal on September 26, with friendlies against Gimnastic Tarragona and Girona taking place in the meantime, and Koeman is delighted to have Messi on board for his maiden season as Blaugrana boss.

"It's great because everybody knows [Messi] is the best player in the world and to have that in your team is exceptional," Koeman told Barca's club media.

Messi returned to training on Monday, and Koeman said: "Okay, for us it's now important to have Leo in the best conditions to play, because there is no question about his quality.

"It's fantastic that he will be part of the season for Barcelona because everybody is really happy about that."

Ivan Rakitic is a big name to have already left Barca in this window, with the midfielder returning to Sevilla, while Luis Suarez has been heavily linked with a move to Juventus.

Sergio Busquets and Jordi Alba are reportedly up for sale, though Koeman is happy with how his squad have been working in pre-season.

"I'm really happy about the performances of the players. They've worked really hard together," Koeman, who is looking to implement a more intense style of play, added.

"We know that it's a pre-season that is a little more complicated because some players have already been playing and some players have had more holidays.

"This pre-season is more difficult to have everybody in the best condition, but we need to play the first game in LaLiga against Villarreal. For that we have some friendlies and more training sessions and we need that because it’s a short period of the pre-season."

The first friendly comes against Gimnastic on Saturday.

Koeman said: "All the players will have 45 minutes – in 45 minutes they need to give intensity, what we like to see in a friendly. To score is not the most important, but yes in a tactical way we've spoken about different things – when we have the ball what we need to do.

"When our rival has the ball, what we need to do to press them and these are all tactical details that we would like to see."