NASA is replacing the lead spacewalker for its next shuttle mission after the veteran astronaut was injured in a bike accident over the weekend, officials said on Wednesday.

Joining the shuttle Discovery crew in place of Tim Kopra will be Steve Bowen, a two-time shuttle veteran who last flew in May. NASA did not immediately say if Bowen's late addition to the crew and training will cause a delay in Discovery's planned February 24 launch on a cargo-delivery run to the International Space Station.

The flight is among the final missions for the space shuttles, which are being retired this year. NASA did not release details of Kopra's injury, citing medical privacy.

"Tim is doing fine and expects a full recovery, however, he will not be able to support the launch window next month," NASA's chief astronaut, Peggy Whitson, said in a statement. "If for some unanticipated reason (the mission) slips significantly, it is possible that Tim could rejoin the crew."

Discovery's launch has been on hold since November to repair cracks in its fuel tank.

The space agency also has a backup crew member in training for its April mission of the shuttle Endeavour, currently scheduled to be the last space shuttle flight.

The commander of that crew, Mark Kelly, is on personal leave to tend to his wife, U.S. Representative Gabrielle Giffords. The Arizona Democrat was critically injured during an attack that killed six people and injured 13 others outside a Tucson grocery store on January 8.

Deputy chief astronaut Rick Sturckow joined the Endeavour crew for training last week. It's launch is targeted for April 19.

In an interview on ABC's 20/20, which aired on Tuesday night, Kelly said he isn't sure he will fly and that his first priority right now is his wife.

"I've flown in space three times. I don't have to do it again. My goal is to make sure that my crew is safe and they can execute this mission safely," he said.

"My number one priority is her. Ideally, I'll have this discussion with her. I'll consider what she says. Hopefully we can make this decision jointly," he said.

NASA is hoping for funding to fly an extra shuttle mission this summer to deliver a year's worth of supplies to the space station. A crew for that flight has already been named.

The shuttles are being retired after 30 years due to high operating costs, ongoing safety concerns and to free up money to develop spaceships that can carry cargo and people beyond the station's 220-mile-high (350-km-high) orbit.

Russia already has taken over the job of flying crew members to the station, a $100 billion project of 16 nations, though the U.S. government is hoping to contract with private companies for crew launch services if any can develop the capability.