Brentford boss Uwe Rosler was furious Barry Corr's second half equaliser was allowed to stand for Southend United.
The Irish striker headed home a right wing free-kick from Kevan Hurst to earn the Shrimpers a 2-2 draw at Roots Hall.
But that came after the Bees defence had rushed out trying to play offside and Rosler felt it should have been disallowed.
"Southend's equalising goal was at least two metres offside," said Rosler. "I went to see the referee after the game because it is not good enough for the linesman to make a decision like that and he should just apologise.
"We are professionals and we expect the referee and his officials to also be professional as well.
"But now we have another game in our already busy schedule which we do not really need at the moment.
"The replay will be hard as well because Southend are a good team. They play clever football which is hard to cope with and Gavin Tomlin up front is an excellent player which makes it even harder for us."
But, early on at Roots Hall, Brentford seemed set for victory. They went in front with a well worked goal in the 29th minute when Tom Adeyemi raced on to a neat flick from Paul Hayes and rolled a low slot in to the bottom left hand corner of the net.
The Bees then doubled their lead nine minutes later when a low right wing cross from Sam Saunders was diverted past his own goalkeeper by Ryan Cresswell at the near post.
However, Southend got back in to the game within 60 seconds when Sean Clohessy's deep cross was the right flank was headed home at the far post by Corr via the underside of the crossbar.