Marc Albrighton insists referee Jonas Eriksson was wrong to award Atletico Madrid a penalty in their 1-0 win over Leicester on Wednesday.
Antoine Griezmann's controversial first-half spot-kick was the only thing separating the sides after the first leg of their Champions League quarter-final in the Spanish capital.
Eriksson awarded a penalty to the hosts when Albrighton brought down the French forward, despite the offence taking place outside the box. The 27-year-old conceded it was a foul but was adamant the official made a mistake.
"I asked the ref about the decision after the game and he said the foul was on the line. That's his verdict on it but TV replays have shown it was outside," he said.
"It was a clumsy challenge but my first thought was to not let him in the box. The final decision lies with the referee and it has cost us. We can't afford to dwell on it and we have to put it out of our minds as soon as possible.
"We've just got to move on although it's taken the gloss off it a little bit."
Leicester boss Craig Shakespeare also criticised the referee for the decision.
He said: "I think it's a real disappointment. It's a key moment in the game. It's a really disappointing decision by the referee.
"He has to get that one right. You can't guess on those ones. It's a free-kick, it's a definite free-kick, but it's outside the box."
Robert Huth received his third caution of the competition and will miss Tuesday's second leg at the King Power Stadium, while captain Wes Morgan is also battling a back injury and remains a doubt, with Yohan Benalouane the only recognised centre-back currently available.
"I've just told Wes in there that when we get back to the hotel, he's getting his kit on, going to the gym and making sure he does a session," Shakespeare added.
"We were always on the tightrope with people like Robert because he's a very competitive centre-half. As you say, it was a very competitive game."
Leicester did not manage a shot on target but Shakespeare believes they have a chance of reaching the semi-finals.
He added: "I've seen enough throughout the squad, through working with them. We know what we're about at the King Power. We know what we've got to do."
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