Barcelona returned to training on Wednesday although it will be a while before coach Ernesto Valverde has his whole squad available once again.
Valverde called on 15 players as his second season in charge at the Camp Nou began with physical tests and assessments.
Sergi Roberto and Nelson Semedo, neither of whom were called up for the World Cup, were the only first-team regulars present at the Ciudad Deportiva in Sant Joan Despi, Spain.
A number of other players who took part in the tests face uncertain futures this summer.
Jasper Cillessen, Rafinha, Paco Alcacer, Lucas Digne, Andre Gomes and Aleix Vidal have all been linked with moves away from the club.
Others -- such as Munir El Haddadi, Sergi Samper, Douglas and Marlon Santos -- return from loans but are unlikely to be around when the season begins in August.
💪✅ Barça 2018-19 is underway 🔵🔴 #ForçaBarça pic.twitter.com/muKsP2vo7R
— FC Barcelona (@FCBarcelona) July 11, 2018
Carles Alena has been promoted to the first team from Barca B but remains sidelined with an injury that will cost him the start of the campaign.
The players that took part in the World Cup will return gradually.
Lionel Messi, Gerard Pique, Jordi Alba, Sergio Busquets, Marc-Andre ter Stegen and Yerry Mina could all feature, at some point, in the tour of the United States after their countries failed to make it past the round of 16.
However, the La Liga champions will have to wait longer for Luis Suarez, Philippe Coutinho, Thomas Vermaelen, Ivan Rakitic, Ousmane Dembele and Samuel Umtiti.
Barca's first game in the U.S. is against Tottenham Hotspur in Los Angeles on July 28, and they then face Roma in Dallas and AC Milan in Santa Clara, California.
Meanwhile, Barca continue to tie down their most promising youngsters to improved contracts.
Left-back Juan Miranda has signed a new three-year deal with a €200 million buyout clause.
Miranda follows, among others, Jandro Orellana, Riqui Puig, Abel Ruiz, Monchu and Oriol Busquets in committing his future to the club as Barca B coach Garcia Pimienta targets promotion back to the second tier.