The pitcher declined comment before Chicago's game against the Pittsburgh Pirates, and Cubs assistant general manager Randy Bush said: "There is nothing to report."
Dempster has the right to refuse any deal.
A message posted Monday on the Twitter account for Dempster's foundation read: "THERE IS NO TRADE don't know where this info came from!"
Dempster is 5-4 with a major league-best 2.11 ERA in 15 starts, making him one of the most attractive pitchers on the market before the July 31 deadline for making trades without waivers. His contract expires after this season, and the fifth-place Cubs entered Monday 18 games below .500.
The right-hander can veto any deal because he has 10-and-5 rights — at least 10 years of major league experience and five seasons with his current club.
Dempster remains scheduled to start Wednesday against Pittsburgh.
Cubs manager Dale Sveum called the trade reports "a fabrication" and added: "For somebody to report it happened, it's very unprofessional to do anything like that in that kind of situation."
A phone message left for Dempster's agent was not immediately returned.