The Russo brothers allude in an interview with Empire that Mark Ruffalo (The Avengers) may return for Avengers: Doomsday. The direct quote from the interview comes from Joe Russo and follows,

I think [what] we could say is, [Banner] is certainly involved in the story that revolves around Doom. We will not confirm nor deny his appearance in Doomsday.

To which his brother Anthony adds,

The farthest we can go is to say, there are characters and actors who have not been announced, who are a part of Doomsday.

The statement can be backed up by the new scene that was recently added to Avengers: Endgame Encore that shows Bruce Banner interacting with Dr. Doom. When asked about the scene and what is Dr. Doom’s intentions with Hulk, Anthony says,

I mean, look, his interest may extend beyond just Banner. So, that’s what we’ll say about that.

Joe adds,

Yeah, you’ve got to save some surprises.

The rest of the interview addresses the other new scenes added to the rerelease, including the scene of Dr. Doom making his mask. The interviewer makes a connection between Tony Stark making his first suit in Iron Man and the new scene and Joe says,

It’s been planned all along. There is certainly a symmetry at play here. There is an interesting examination of good and evil at play. And I think that that scene at the end, obviously it’s intended to be almost identical. It’s because there’s a duality being explored.

Avengers: Doomsday is set to release in theaters everywhere on December 18th.