An ultrasound found that Nadal had an "acute rupture of his right abdominal muscle" that will require physiotherapy, rest and medication for "two to three weeks," the chief doctor of the Spanish Tennis Federation said in a statement released by tournament organizers on Monday.
The Thailand Open runs from Sept. 26-Oct. 4.
Nadal has expressed his disappointment for the cancellation and being unable to take a planned pre-tournament vacation to the Thai island of Krabi, the statement added.
Nadal sustained the injury during the U.S. Open earlier this month, where he lost his semifinal in straight sets to Juan Martin del Potro. The Argentine went on to capture his first Grand Slam title with an upset victory over top-ranked Roger Federer in the final.
The injury also forced No. 2-ranked Nadal to sit out Spain's Davis Cup semifinal win over Israel on the weekend.
Nadal has struggled with injuries this season, with sore knees keeping him off tour for all of June and July - forcing him to skip a title defense at Wimbledon - and the abdominal muscle issue flaring up during his third-round victory over Nicolas Almagro at the U.S. Open.
Senna blowNadal not in peak condition heading to US Open
