NASA said Thursday that it will bring four astronauts aboard the International Space Station back to Earth more than a month earlier than planned.

The space agency said Wednesday that it was postponing Thursday’s planned spacewalk because of a medical issue with one of the astronauts.

Citing medical privacy concerns, NASA did not provide additional details, including the identity of the affected crew member, the nature of the medical issue or its severity.

“After discussions with chief health and medical officer Dr. JD 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 Administrator Jared Isaacman said at a news briefing.

In an update early Thursday, NASA had said that the situation was stable but that officials were weighing whether to bring several of the astronauts back to Earth earlier than planned — a rare move.

“Safely conducting our missions is our highest priority, and we are actively evaluating all options, including the possibility of an earlier end to Crew-11’s mission,” NASA officials wrote in a blog post.

The Crew-11 mission launched to the space station on Aug. 1, carrying NASA astronauts Zena Cardman and Mike Fincke, Japanese astronaut Kimiya Yui and Russian cosmonaut Oleg Platonov aboard a SpaceX Crew Dragon capsule. The four were expected to remain aboard the orbiting laboratory until late February.

This article was originally published on NBCNews.com