The team later confirmed Rapoport's report.
By using the transition tag as opposed to the franchise tag, other teams will have the opportunity to make an offer for the Pro Bowl center in free agency.
The Browns can match any competing offer within five days. The transition tag lowers Mack's one-year price tag from $11.6 million to approximately $10 million.
Mack is Cleveland's No. 1 free-agent priority. He's been remarkably durable, playing every offensive snap over the course of his first five seasons. ProFootballFocus.com ranked Mack as the fourth-best center in football last season.
The transition tag decision comes after the two sides met this weekend. The purpose of the meeting was for Mack to get more acquainted with the new coaching staff and administration.