Atlanta is set to watch Tomas in the near future, the report says.
Heyman writes that while the San Diego Padres, San Francisco Giants and Philadelphia Phillies are believed to be aggressively pursuing Tomas, recent talks suggest a "mystery team" could be in the running for the 23-year-old.
Philadelphia has reportedly "cooled" on the idea of signing Tomas.
A previous report said that Tomas could wait until the MLB winter meetings -- which run from Dec. 8-11 -- to sign with a team. According to Heyman, Tomas is targeting a contract larger than the six-year, $72 million deal the Red Sox reached with fellow Cuban outfielder Rusney Castillo this summer.