The fight is pencilled in to take place at London's O2 Arena on October 8, and Benn's promoter Eddie Hearn is already claiming it will be 'one of the biggest fights of all time'.
Benn fights at welterweight while Eubank Jr is a middleweight but they have agreed to an 11st 2lb catchweight. However, they are now locked into a dispute over how much weight they can put on between the weigh-in on Friday and the day of the fight.
The clause would be in place to stop Eubank Jr having a big size advantage after rehydrating. Benn's team will want as low a weight as possible, while Eubank Jr's camp would probably request no rehydration clause at all.
The winner of the potential fight could scoop up to £7million depending on ticket sales and pay-per-view on DAZN.
If the fight does not go ahead Eubank Jr could set up a fight with fellow Brit Liam Smith, while Benn's other opponent could be former world welterweight champion Keith Thurman.
Benn and Eubank Jr are the sons of two former world champions, Nigel Benn and Chris Eubank, who fought twice during the early 90s when British boxing was at the peak of popularity.