Juventus lost summer signing Sami Khedira to injury as the Italian champions went down 2-0 to Marseille in a friendly at the Stade Velodrome on Saturday night.
German international midfielder Khedira joined Juve from Real Madrid in the close season after seeing the latter part of his time at the Santiago Bernabeu marred by injury problems.
And the 28-year-old was forced off just past the midway point in the first half of the game in France, grimacing in pain as he departed holding his right hamstring.
Italian media reports indicated that Khedira will be out for a month, which would rule him out of next week's Supercup against Lazio and the start of the new Serie A season on August 23.
On a disappointing night for Massimiliano Allegri's side, a Romain Alessandrini cross surprised Gianluigi Buffon to give OM the lead late in the first half.
Abdelaziz Barrada got the hosts' second goal in front of a crowd of more than 64,000 while Juve had Stephan Lichtsteiner sent off just before the break for dissent.