Nasa has announced when it will commence its first medical evacuation from the International Space Station after an astronaut fell ill with a “serious” but undisclosed issue.

The US space agency announced on social media on Friday night that it will aim to have the crew leave the station no earlier than 5pm EST on Wednesday, 14 January, with the goal of them landing near California early on Thursday morning, 15 January, “depending on weather and recovery conditions”.

“After discussions with chief health and medical officer Dr James Polk and leadership across the agency, I’ve come to the decision that it’s in the best interest of our astronauts to return Crew-11 ahead of their planned departure,” Nasa’s administrator, Jared Isaacman, said at a briefing on Thursday.

This is the first medical evacuation from the space station in its 25-year history. An astronaut in the orbital laboratory reportedly fell ill with a “serious” but undisclosed issue. Nasa also had to cancel its first spacewalk of the year.

“This was a serious medical condition,” Isaacman said. “That is why we’re pursuing this path.”

The agency did not identify the astronaut or the medical problem, citing patient privacy.

“Because the astronaut is absolutely stable, this is not an emergent evacuation,” Polk said. “We’re not immediately disembarking and getting the astronaut down, but it leaves that lingering risk and lingering question as to what that diagnosis is, and that means there is some lingering risk for that astronaut onboard.”

Crew-11, led by US commander Zena Cardman, arrived on a SpaceX capsule in August. The group also includes Nasa astronaut Mike Fincke, Japanese astronaut Kimiya Yui and Russian cosmonaut Oleg Platonov.

Three others, US astronaut Chris Williams and Russia’s Sergei Mikayev and Sergei Kud-Sverchkov, will continue living and working at the station.

Nasa plans to bring the ageing space station, which is expensive to operate, out of orbit by late 2030 or early 2031.