The Russian chief arms control negotiator also noted that Russia would refuse any agreement on the New START that was timed to coincide with the US presidential election.
The president appeared on Fox's Tucker Carlson Tonight for what the White House described as an on-air "medical evaluation" conducted remotely by Fox contributor doctor Marc Siegel.
Polls show Biden leads heavily in key demographics including women and the elderly, prompting analysts to talk increasingly of a possible landslide victory.
Trump was eager to return to the campaign trail, telling aides that he wanted a series of mega rallies in Republican-friendly areas in battleground states to mark his recovery.