49ers Enterprises, the investment arm of the NFL franchise San Francisco 49ers, have been a shareholder at Leeds, recently relegated from the Premier League, since their initial investment in May 2018.
Over the last few years, their stake increased to 44%, while Radrizzani's Aser Ventures owned the remaining 56 percent. Leeds said that a purchase had now been agreed.
"Both parties continue to work through the details, and further updates will be provided soon," said a statement.
Earlier this season, Radrizzani and his partner Matteo Manfredi made a purchase of the relegated Serie A club Sampdoria.
Leeds were relegated from the top flight this season after a roller-coaster season under four different managers. They finished second from bottom in the standings on 31 points.
"All of our focus remains on a quick return to the Premier League," the statement added.