The Perseverance rover and its associated mission will cost about $3 billion. It will look for signs of Martian life in the past, as well as gathering materials from the surface that will one day be returned to Earth.
The launch has been pushed back to 30 July at the very earliest, the space agency announced, leaving it with only half the expected launch window.
Nasa must send the rover and the rocket carrying it into space by 15 August, or Mars will move too far away for the mission to be launched at all.
If that happens, engineers will have to wait until 2022, when the planets will align in the right way once again.
The space agency said that it hopes to be able to push back the window, giving it more time to attempt the launch, to avoid the 26 month delay that could come with any further problems.
Nasa has already been forced to delay the launch, in part because of contamination problems and issues with a crane at the pad. It had originally been scheduled to go as soon as 17 July, before being pushed further and further into the month.
United Launch Alliance, which made the rocket that will carry the rover to the red planet, said that it needed extra time to deal with problem readings during a recent practice for the launch, the space agency said in a release. A liquid oxygen sensor line had shown unexpected readings during that rehearsal, it said.
Whether or not Nasa is forced to delay, it will aim to send the rover to a river delta on the Martian surface, where it will begin the work of exploring the surface.
The European Space Agency has already been forced to push its own launch back until 2022, in part because of issues arising from the coronavirus pandemic. The United Arab Emirates and China are also planning missions to Mars during this window, and their launches are said to be on track.