The developer told the Los Angeles Times he doesn't know McMahon personally, but acted out of compassion because helping out "would be an honor."
McMahon, 85, who was Johnny Carson's sidekick on the "Tonight" show for three decades, has not worked for about 18 months because of a neck injury. He defaulted on $4.8 million in mortgage loans with Countrywide Financial Corp.
McMahon's spokesman, Howard Bragman, told The Associated Press that paperwork on the sale had not been completed but that McMahon was "very optimistic" the deal would go through.
"When I was at the Wharton School of Business I'd watch him every night," Trump told the Times. "How could this happen?"
McMahon bought the six-bedroom, five-bathroom, 7,000-square-foot house in January 1990. The home was listed at $4.6 million last weekend - down from a peak price of $7 million.