Leeds United head coach Thomas Christiansen has criticised referee Simon Hooper's performance in their 2-1 home defeat by Derby County.
The hosts led through Pierre-Michel Lasogga before Sam Winnall's second half double for the Rams.
"If you play against 12 it is very difficult," 44-year-old Christiansen told BBC Radio Leeds.
"It's clear we should have had a penalty and their penalty was a foul outside the box. You feel impotent."
He continued: "The game would have changed totally if we'd got a penalty because it was a red card.
"I don't want it to be an excuse but I'm upset and sad for my players because with the effort they have put in we didn't win because of those situations."
Tuesday's defeat meant Leeds have now lost six of their last seven games in all competitions.
Christiansen, who was appointed as Garry Monk's successor in June, said he understood supporters feeling frustrated.
"It's normal fans will be angry. It's another defeat but I can not say anything against the players because they tried their best," the Dane added.
"I'm worried about the results, it's a bad situation but I believe there's not a big difference between the good moments and the bad moments."