The 25-year-old joined Middlesbrough in the summer of 2017 when he moved from Forest for a transfer fee reported by BBC Sport to be worth £15 million. It has been reported that Boro will not allow their star striker to leave the Riverside Stadium on the cheap this summer.
The Congo international has a superb goalscoring record, and he did continue his impressive form at his new club last season, scoring 15 goals in 34 Championship starts.
The report claimed that Championship rivals Birmingham City and Swansea City are interested, while Nottingham Forest are keen to bring their former player back at City ground.
Furthermore, it will be difficult to lure him away from Riverside given Boro themselves will be looking to challenge for play-off places next season.
However, if Leeds do manage to fork out a deal for Assombalonga it would represent a massive signing for the club.
With him in the side, goals are guaranteed. He is a proven Championship striker and has the ability to win matches singlehandedly. Leeds need a striker who can score 15-20 goals in a season, and Assombalonga could be that man for them.