HOUSTON — Atlantis shuttle astronauts took a close look at a torn insulation blanket on their vehicle's engine pod Sunday as mission managers officially extended their flight by one day due to a crew member?s illness.

John Shannon, NASA's deputy shuttle program manager, said Atlantis? now 12-day mission to deliver a new European lab to the International Space Station (ISS) was extended to make up for lost time. An undisclosed medical issue among Atlantis' crew Saturday prompted a 24-hour delay for a spacewalk originally scheduled for today.

European Space Agency (ESA) astronaut Hans Schlegel, a German spaceflyer, was replaced by U.S. crewmate Stanley Love for the upcoming spacewalk after the medical issue arose, but is expected to rejoin the spacewalking rotation later this week as per the mission plan, said NASA's STS-122 shuttle flight director Mike Sarafin.

"The plan right now is to perform the rest of the mission as planned," Sarafin told reporters in an afternoon briefing here at the Johnson Space Center (JSC). "The timeline changes that we've had to make aren't going to result in any impact to the mission."

While the U.S. space agency refrained from commenting on the nature of the illness or whom it afflicted, ESA officials revealed some details earlier today on their blog chronicling Atlantis? mission to deliver the European Columbus laboratory to the ISS.

"Hans Schlegel went into space in perfect health condition," wrote Volker Damann, head of the ESA's Crew Medical Support Office, in mission update posted to the blog. "However, he has developed a condition that is neither life threatening nor does it impact the health of other crew members — but is currently not compatible with a space walk (EVA)."

ESA officials said they were confident Schlegel would be ready for the second of three planned spacewalks for Atlantis' STS-122 mission. That spacewalk, also to be performed alongside Walheim, is now scheduled for Wednesday.

The shuttle astronauts launched on Feb. 7 and are now expected to land on Feb. 19.

Shuttle crew inspects torn shuttle blanket

With their first spacewalk delayed to Monday, Atlantis astronauts squeezed in an extra inspection of their shuttle's heat shield to take a closer look at a small torn piece of insulation.

The small, uplifted piece of torn fabric is located on the shuttle's right rear-mounted engine pod, and is one of the few remaining outstanding items for analysis related to the health of Atlantis' vital heat shield.

"We have completely cleared the bottom of the orbiter," Shannon said, adding that the heat-resistant carbon composite panels along Atlantis' nose and wing edges are also in fine shape.

Aside from the slightly torn blanket and a few chipped heat-resistant tiles around Atlantis' windows, the spacecraft appears to be in good health, he added.

"The team has taken this somewhat unexpected day inserted before the [spacewalk] and made great use of it," Shannon said.

NASA is broadcasting Atlantis' STS-122 mission live on NASA TV. Click here for SPACE.com's shuttle mission coverage and NASA TV feed.