The Championship side sent their FA Cup fifth round tie to extra-time thanks to a Sammie Szmodics’ 79th minute strike.
However, supporters believe they have spotted an infringement in the build-up.
Arnor Sigurdsson had latched onto a long throw after Jamaal Lascelles misjudged the flight of the ball.
He teed up Dilan Markanday, whose effort was tipped onto the bar by Martin Dubravka, only for Szmodics to convert the rebound.
Replays appeared to show that play should have been pulled back to the initial throw-in, though, due to a raised boot from Billy Koumetio.
Players must have part of both feet on the floor when the ball is released, which replays suggested Koumetio did not.
Reacting to the goal on X, one fan wrote: “No one pick up on the foul throw from the Blackburn player in the lead up to their goal? No? Just me then.”
Another added: “Anyone else spot Blackburn’s foul throw in the build up to the goal?”
Meanwhile, a third fan also added: “Love a good old fashioned foul throw.”
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With no VAR in operation at Ewood Park, the goal was allowed to stand after the alleged foul throw was not pulled up by the officials.
Neither side were able to break the deadlock in what remained of the 90 minutes as the match headed to extra-time.
The winner of the tie will join Coventry, Leicester and Manchester City in Wednesday’s quarter-final draw.