NASA is considering ending a mission on board the International Space Station early after an astronaut suffered a medical emergency.

The US space agency said Wednesday it could curtail the Crew-11 mission in a rare move, which involve astronauts from the US, Japan and Russia, after postponing a Jan 8 spacewalk in light of the emerging health concern.

“Safely conducting our missions is our highest priority, and we are actively evaluating all options,” NASA said in a statement.

The incident involved a single unidentified crew member, who is currently in a stable condition. NASA said it would provide a further update within 24 hours.

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The Crew-11 mission started in August last year, using SpaceX’s Crew Dragon Endeavour capsule. The team on the mission consists of NASA astronauts Zena Cardman and Mike Fincke, Japan Aerospace Exploration Agency’s Kimiya Yui and Roscosmos cosmonaut Oleg Platonov.

The next team of four members involved in NASA’s SpaceX Crew-12 mission was due to launch on Feb 15 at the earliest, the space agency said previously.

Spacewalks are a crucial part of ISS missions, partly to check and maintain the aging space infrastructure. The orbiting laboratory is due to be decommissioned in 2031 at the latest in light of its advanced age and rising maintenance costs.