Thomas, 29, is expected to be one of the two most sought-after free agents this year along with Bills cornerback Nate Clements.
"We're working on it," Ravens president Ozzie Newsome said of the team's efforts to keep Thomas, who had a career-high 11 sacks last season and has 28 over the past three years.
Newsome left open the chance that Thomas would be tagged as a franchise player, effectively taking him off the free agent market. Franchise players still are allowed to negotiate with other teams, but their original clubs have the right to match any signed deal or receive two first-round draft picks as compensation if the player changes teams.
"That's going to come down to the 11th hour," said Newsome, who'll have until 4 p.m. on Thursday to decide whether to franchise Thomas.
Bus Cook, Thomas' agent, said he and the Ravens "aren't close" on a possible contract.
If Thomas is declared a franchise player, he would likely be the seventh player to be tagged this season. Bears linebacker Lance Briggs, Patriots cornerback Asante Samuel and defensive ends Charles Grant of New Orleans, Dwight Freeney of Indianapolis and Justin Smith of Cincinnati have all been given that designation.
In addition, Lions defensive lineman Cory Redding is expected to be franchised. The only remaining issue was whether Redding would be declared an end or tackle.