Lionel Messi has been ruled out of Barcelona's opening pre-season friendly against Hamburg through injury.Messi, 25, has suffered a calf strain and therefore was not part of the 21-man squad that travelled to Germany for Tuesday evening's friendly.Barcelona's medical staff have said that Messi's availability for upcoming matches depends on how he responds to treatment.Tito Vilanova's side are due to face Raja Casablanca in a friendly in Morocco on Saturday before taking on Espanyol in the Catalan Supercup next Tuesday. They then play friendlies against big-spending Paris St Germain and Manchester United on August 4 and 8, respectively."I'm sorry for the people of Hamburg who have bought tickets," Vilanova told a press conference of Messi's absence. "It was a last-minute thing. He's a player who always wants to play and he more than anyone regrets that he is unable to be here. Hopefully he will be back for Saturday."