Professor Hulk's arm got seriously injured in Avengers: Endgame and it has been confirmed by the Russos that it is permanent.
The character of Hulk has been through a lot in the last two Avengers movie. From getting his a$$ whooped, to losing the love of his life to losing his arm. It's all been downhill for the not-so-incredible Hulk and we can't help but feel for him. In the third act of Avengers: Endgame professor Hulk wears the gauntlet and snaps his fingers, undoing Thanos' initial snap. As a result, his arm gets seriously injured.
I thought to myself that professor Hulk would soon heal and be back to smashing things but it seems like the days of the old Hulk are over. The Russo brothers have gone on record to say that professor Hulk's injuries in Endgame are permanent. Co-director Joe Russo told Comicbook.com:
“He’s lost an arm. He lost Natasha. That’s not coming back. He’s damaged himself. I don’t know. It’s interesting. That’s permanent damage, the same way that it was permanent damage with Thanos. It’s irreversible damage. His arm, if you noticed, is a lot skinnier. It’s blackened. So, he loses a lot of strength there.”
But it's not completely hopeless for professor Hulk as Joe Russo went on to mention that the MCU has a lot of really intelligent scientists and doctors who can patch up professor Hulk to be as good as new.
But who knows? There’s a lot of smart people left. Maybe someone helps him repair that. Maybe someone gives him a new arm. I have no idea where that character goes from here. The nice thing is we didn’t have to pay attention to where it goes after this, we just try to tell a satisfying ending.
We do know that Mark Ruffalo will be returning in a She-Hulk/Hulk TV show and I assume that it will address professor Hulk's arm