Lionel Messi is set to miss Barcelona’s upcoming trip to the USA after suffering a calf injury during his first training session back at the club.Having been given extended leave following Argentina’s run to the semi-finals at this summer’s Copa America, Messi only returned to the fold on Monday.However, he was forced to pull out of the session with what doctors have diagnosed as a grade one calf strain. Article continues below Editors’ Picks Emery out of jail – for now – as brilliant Pepe papers over Arsenal’s cracks What is Manchester United’s ownership situation and how would Kevin Glazer’s sale of shares affect the club? Ox-rated! Dream night in Genk for Liverpool ace after injury nightmare Messi a man for all Champions League seasons – but will this really be Barcelona’s? August has not been an easy month for Messi so far. Last week, it was announced that he would face a three-month suspension from international football plus a heavy fine after his controversial comments about perceived favouritism towards Brazil at the Copa America .He joined back up with his club team-mates over the weekend and watched from the bench as they came from behind to beat Arsenal in what was the Gunners’ final game of pre-season.Initially trailing to Pierre-Emerick Aubameyang’s superb strike, Barca levelled thanks to a comical mix-up between Bernd Leno and Ainsley Maitland-Niles before Luis Suarez won it at the death.Messi may have been hoping to feature in one of their upcoming fixtures in the USA but is now facing a nervous wait to see when he will be available with the new La Liga season less than two weeks away.Barca face Napoli twice in the USA, with fixtures in Miami and Michigan, before starting the new campaign with a trip to Athletic Club on August 16.Manager Ernesto Valverde has at least been boosted by the return to training of the other members of his squad to have played at the Copa America.Arturo Vidal and Philippe Coutinho are back in the picture and are included in the travelling squad, as well as new signing Junior Firpo.The 22-year-old left-back signed on a five-year deal from Real Betis for a fee of €18 million (£16.3m/$20m). Taking on the number 24 shirt, he will provide much-needed competition for veteran left-back Jordi Alba.Four Barcelona B players who have been in among the first-team squad during pre-season will also travel to the USA. Inaki Pena, Riqui Puig, Carles Perez and Abel Ruiz will all be hoping to impress Valverde and get some minutes under their belt against Napoli.