However, Leeds are not the only club keen to sign. The report suggests that Championship rivals Birmingham City and Swansea City are interested, while Nottingham Forest are keen to bring their former player back at City ground.
Assombalonga 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 likes of Forest and Leeds will be aiming to win promotion from the Championship to the Premier League next season, and Assombalonga will be a massive signing for the club.
With Boro themselves aiming to finish in the play-off places of the Championship next season, it will be extremely difficult for the likes of Leeds and Forest to convince them to sell the the striker to a direct rival.
The 25-year-old Congo international has a superb goalscoring record, and he did continue his impressive form at his new club, scoring 15 goals in 34 Championship starts.
Forest have been very active in the summer transfer window, and they have signed Lewis Grabban on Friday. He has joined for an undisclosed fee from Bournemouth, believed to be in the region of £6 million, and it remains to be seen whether Aitor Karanka will still push for a move for Assombalonga.