"Personally, I think he made a deal with Hillary, where ... he gets a job," the Republican presidential nominee said in an interview airing Sunday on ABC News' "This Week."
Though not affiliated with either major political party, Bloomberg endorsed Clinton and spoke on the final night of the Democratic National Convention in Philadelphia. In his speech, the billionaire media mogul called Trump "a dangerous demagogue" and criticized his business record.
"Trump says he wants to run the nation like he's run his business. God help us," Bloomberg said.
But speaking with ABC host George Stephanopoulos, Trump criticized Bloomberg's decision not to mount an independent run for president though he "wanted to run for president for probably as long as you've known him."
"He never had the guts to do it. And now I see this guy up onstage saying negative things," Trump said. "He knows nothing about me. He's never been to my office. I don't know him well."
The New York real estate mogul and entertainer also hit Bloomberg for spending millions of his personal fortune to win a third term as mayor of New York and criticized his final term in office. Bloomberg, he said, "couldn't get elected dogcatcher in New York."
"He spent a fortune to get elected. He shouldn't have gone to third term," he said. "The snow removal was a disaster. He had a lot of problems."
Stephanopoulos pointed out, however, that the two moguls golfed together, which Trump said happened "maybe once."
"And I hit the ball a lot longer, a lot better," Trump added.
Comment: "See, I'm better than Bloomberg!!"
Bloomberg's a bully. When he speaks of dangerous demagogues he is looking at his reflection.
IMHO, America needs a period of quiet reflection and restoration. Mr Trump wants to focus his efforts on making America great; he wants to leave a healthy legacy. Mr Bloomberg seeks personal power, privilege and profit. He has never experienced losing everything and having to start from scratch again to rebuild; Mr Trump has picked himself up several times; he knows how to do rebuild.