Officials for NASA say one of the tasks remained uncompleted because some cables couldn't be successfully connected.
Flight director for NASA Heather Rarick said that the work would be completed some time in the future and might be carried out on the Atlantis flight which is scheduled for November.
Discovery is due to take off on Tuesday and should be back in Florida by Thursday.
The spacewalk took seven hours and NASA say that the two astronauts, Danny Olivas and Christer Fuglesang, finished all of their most important tasks during the work.
The two astronauts unwrapped 18m of cable ready for the introduction of a new room which will be added to the space station early in 2010.
Two antennas for a Global Positioning System were also added along with some additional electrical equipment.
Towards the end of the task one thing didn't go quiet to plan. The astronauts weren't able to hang a connector to part of the space station.
This problem escalated when the helmet camera belonging to Christer Fuglesang began to loosen and controllers were left unable to see the astronaut work.
Mission Control said: "We thought you were doing tremendous acrobatic