HOUSTON -- Astronauts at the International Space Station Sunday got back on track preparing for a space walk after a German astronaut fell sick, forcing the exercise to be delayed for 24 hours.

NASA said earlier that Hans Schlegel had recovered from the unidentified ailment, and that the space walk was on schedule for Monday.

Schlegel nevertheless was pulled off the walk, which is to begin hooking up the European Columbus science research module delivered to the ISS aboard the US Atlantis space shuttle. He will be replaced by US astronaut Stanley Love, who will join Rex Walheim on the exercise.

Schlegel, one of seven astronauts, including two Europeans, who rode the Atlantis up to the ISS, was reported ill just after the shuttle docked Saturday at the space station, two days into the mission.

But early Sunday Markus Bauer, the spokesman for the European Space Agency, said Schlegel, 56, appears to have recuperated and was doing "very well".

"We are assuming that he will take part in the second space walk," said Bauer.

While Schlegel's ailment remains unexplained, the German astronaut -- who joined a shuttle mission in 1993 -- spoke to Mission Control in Houston after waking up shortly before 1000 GMT Sunday.

"Greetings to everybody in America, in Europe and in Germany, and especially of course to my close family and my lovely wife, Heike." he said.

The space walk will now take place at 1435 GMT Monday, and last about six and a half hours.

Walheim and Love will have to spend a night in a decompression chamber ahead of the walk to purge nitrogen from their bodies, NASA said.

They spent Sunday preparing their spacesuits, while others aboard the ISS transferred supplies from the Atlantis.

On Sunday the astronauts were also to use a camera attached to a robotic arm to inspect a 3.25 centimeter (1.3 inch) tear in the thermal blanket on the shuttle's right Orbital Maneuvering System pod.

The damage occurred during the launch Thursday and was discovered the next day, according to shuttle flight director Mike Sarafin.

The delay to the first space walk has forced the National Aeronautics and Space Administration to extend the original 11-day mission of the shuttle Atlantis by one day, setting its return to Earth on February 19.

The Atlantis mission to deliver the 10-ton Columbus laboratory marks a milestone in Europe's role in space. Paid for mostly by Germany, Italy and France, it is the first ISS addition not made in the United States or Russia.

The laboratory will be used for biotechnology and medicine experiments involving microgravity.