Could Dirrell/DeGale be added to the undercard ? Maybe

Unlikely but DeGale think there is a possibility

"I've not been chopping wood like Mayweather has but I like it, it's old school and Mayweather is an old school type of fighter and I've seen how he trains at his gym.
I've been doing all kinds of different things in training, sprints on the track to two hours runs up Hampstead Heath as well as working in the gym.
I've trained at St George's Park [the FA's National Football Centre and home of the England football teams in Burton] and I'm going to be spending a week up there for my fitness because they have got great facilities. They have a hydro pool, an altitude chamber, sports scientists and they have even put some bags up for me. It's going to really help.
I've not got a date yet but I think they have to let me know by next Tuesday. There were rumours it was going to be in Chicago on April 24, but I've been told it's definitely not going to be then, so maybe it will mid May sometime.
Eddie [Hearn] was looking at putting it on in London on April 25 so I'm seven weeks into training camp anyway, so the quicker it happens for me the better.
There's a little chance it could be on the Mayweather-Pacquiao undercard in Las Vegas on May 2. I would love that obviously but I doubt it; I think they would've announced it if it was."

James DeGale ready for Andre Dirrell, even if it's on the undercard of Floyd Mayweather and Manny Pa | Sport Inside Boxing | ESPN.co.uk