According to AZCentral.com, the Cardinals were making positive steps on reworking the deal for Mathieu, who would have $18 million of his contract guaranteed if he is still on the roster Wednesday.
Mathieu said last week that the team had asked him to take a pay cut. He signed a five-year contract extension in 2016, with $21 million in guaranteed money.
Mathieu's agent, Tom Condon, also represents quarterback Sam Bradford, who reportedly agreed to a one-year deal with the Cardinals on Tuesday.
Arizona is looking to lower Mathieu's cap number of $14.1 million for 2018, the report said.
In 2017, Mathieu played in all 16 regular-season games and recorded 70 tackles and two interceptions. He finished the previous two seasons on injured reserve, although he was named to the Pro Bowl in 2015.