McMahon reports that Villanueva's contract does not include any guaranteed money.
An earlier report from RealGM's Shams Charania said Villanueva was deciding between offers from the Mavericks and Clippers.
Villanueva, 30, is entering his 10th season in the NBA. He spent the past five seasons with the Detroit Pistons after signing a five-year, $37.7 million contract with the team in 2009.
Villanueva averaged 9.5 points and 3.8 rebounds during his time in Detroit, though his averages in both categories declined every season. The Connecticut product played just 20 games last season.
The Mavericks have 15 players on guaranteed contracts, the roster limit for the regular season.
- Ben Estes