The 10-year deal with Nike could reach up to $300 million, with a $50 million retirement package, USA Today reported. This surpasses an Under Armour offer for the Oklahoma City Thunder superstar's endorsement estimated to be worth $250 million to $285 million.
Under Armour is looking to advance its share of the lucrative footwear sector, and it sees basketball as a valuable market, the Baltimore Sun reported. The sports apparel maker signed Golden State Warriors star Stephen Curry away from Nike in 2013.
Retail sales of Durant's Nike shoes netted $175 million in the past year, the Sun reported.
Under Armour did score a key endorsement on Tuesday, however, with ESPN reporting that model Gisele Bundchen will be part of its women's campaign.
The Baltimore-based company released a video Tuesday morning, teasing the model's involvement with the brand with the slogan "I Will What I Want," and promising to reveal more on Sept. 4.
ESPN reported that Under Armour's women's sales account for about 30 percent of its business—at $500 million. The apparel-maker's women's campaign launched last month.
—By CNBC staff