Canadian astronaut Chris Hadfield took to his Twitter account to announce the proposed spacewalk, CNN reported.
"Good Morning, Earth! Big change in plans, spacewalk tomorrow, Chris Cassidy and Tom Marshburn are getting suits and airlock ready. Cool!" he posted.
A decision on whether to go forward with a spacewalk isn't expected until late Friday, NASA said.
The leak in a cooling loop in a solar array that provides power for the station was seen by the crew, which reported seeing small white flakes floating away from the station, the space agency said.
The coolant for the power channel, one of eight used to supply electricity to the station, is likely to be exhausted sometime Friday and the channel will be shut down, NASA said.
Other power sources would be rerouted so that all systems remain fully operational, the space agency said.
Apart from the leak, the station is operating normally, it said.