Slavisa Jokanovic says referee Stuart Attwell made a "costly mistake" during Fulham's 1-1 draw with Reading.
An entertaining Championship play-off semi-final first leg ended all square after Tom Cairney cancelled out Jordan Obita's opener.
But the Whites boss felt the visitors' goal should not have stood.
Stefan Johansen felt he was fouled in the middle of the park, before Reading's Danny Williams was then sent tumbling to the floor.
Neither was signalled as a foul by referee Attwell, but Williams felt he should have had a foul and clearly handled the ball on the floor before Reading broke and eventually scored through a fine left-footed Obita strike.
The Fulham manager was not impressed.
He said: "It can be a free-kick. They touched the ball with a hand. It's a physical, complicated game.
"Sometimes referees make mistakes. It was a costly mistake for us."