NASA managers said they were also considering an unprecedented and complicated last minute repair at the launch pad to replace ill-fitting bolts that anchor the shuttle's main communications antenna to the cargo bay wall.
Wayne Hale, the shuttle program manager, said it was likely the bolts would have to be changed.
Atlantis' mission will be the first shuttle flight to resume construction of the $A131 billion space station since the shuttle Columbia fell apart over Texas in 2003.
Two shuttle missions conducted since Columbia tested safety upgrades designed to avoid a repeat of the accident, when falling insulation foam from the external fuel tank knocked a hole in the shuttle's wing on liftoff.
Superheated atmospheric gases tore into the breach two weeks later upon reentry .
Construction of the space station has been on hold because the US shuttles are the only spacecraft capable of carrying its larger components into orbit.
Resumption of the assembly of the orbital outpost, a multi-nation project, became possible after the safe return to Earth last month of space shuttle Discovery.
Concerns about bolts
While NASA managers said they were confident Atlantis would be ready by August 27, repair work on the bolts could become complicated.
Engineers found the problem after the shuttle was taken to the launch pad for final flight preparations.
Two of the four bolts that hold the Ku-band antenna in place do not meet specifications for flight, though the ship has been flying with the ill-fitting hardware since its first mission in October 1985.
NASA is concerned that if the bolts come loose, the antenna could crash down inside the 18 metre payload bay during launch, with potentially catastrophic results.
Similarly faulty material aboard the space shuttles Discovery and Endeavour have previously been replaced.