The Argentine superstar has been ruled out of his club's first pre-season friendly as a precaution after a taking a knock in a training session and will not join the squad
The 25-year-old strained his right calf during a workout session and the Blaugrana have decided not to risk the Argentine in the friendly at the Imtech Arena.
A statement on the club's official website read: "In training on Monday, Messi strained his right calf. Echography conducted on Tuesday morning has revealed that he has suffered intramuscular bruising and the medical services have said that his availability for future matches depends on how the injury develops."
Messi will now undergo physiotherapy to treat the injury and therefore the squad travelling to Hamburg for Tito Vilanova's first match in charge of Barcelona this season has been reduced to 21 players.
It had been reported that Hamburg will not pay Barcelona €1.2 million (£940,000) in appearance fees for the friendly as stipulated in the match agreement if Messi does not feature.
The game against Thorsten Fink's side is due to kick off at 18:00CET.