Per Yahoo Sports' Shams Charania, Ferrell's agent said they had reservations about the original agreement and want to evaluate where things stand.
"We felt uncomfortable and will weigh our options," Cervando Tejeda said.
Per ESPN's Tim MacMahon, the Mavericks didn't hear from Tejeda regarding Ferrell's status until after seeing Charania's report on Twitter.
Ferrell was set to be the Mavericks' backup shooting guard at the start of the 2018-19 season.
The Mavs rescinded their qualifying offer to Ferrell on July 14, making him an unrestricted free agent, but MacMahon noted they intended to re-sign the 25-year-old.
Wesley Matthews, Dennis Smith Jr. and rookie Luka Doncic are among the backcourt players for Mavs head coach Rick Carlisle to use in his rotation next season.
Ferrell joined the Mavs in January 2017 and has appeared in 118 games over the past two seasons for Dallas. He averaged 10.2 points, 3.0 rebounds and 2.5 assists per game in 2017-18.