Sunderland head coach Regis Le Bris spoke to BBC Radio Newcastle after the Black Cats beat Derby County 1-0 at Pride Park.
"I don't know, really [about why Isidor's goal was disallowed].
"Maybe with VAR we could analyse the first ball and maybe an offside, but I don't think it was that decision. It was higher up the pitch and at the moment we don't know.
"It could have changed the outcome of the game, but at the end it was another tough game and the balance was different for the duration.