Kalil missed all of last season with a knee injury. He started all 16 games at left tackle in 20 17, his very first season at Carolina after enrolling a five-year contract with the team being a free agent.
He spent the first five seasons of his career with the Minnesota Vikings, who selected him fourth overall at the 2012 draft.
He had been a Pro Bowl selection in his rookie season and has started every one of the 82 games he has played at the NFL.
The Panthers will save 7.25 million in the salary cap if they surpass him a post-June inch designation.