Rafa Benitez says it was "not clear" whether Jamaal Lascelles should have been sent off against Liverpool.
Lascelles captained Newcastle United in yesterday's 2-0 defeat at Anfield.
The defender brought Mohamed Salah – who had opened the scoring with a first-half goal – down in injury time.
Lascelles's challenge came just outside the box, but he did appear to deny Salah a clear goalscoring opportunity.
Referee Graham Scott's failure to penalise Lascelles infuriated Liverpool manager Jurgen Klopp, who also felt that Salah should have had a penalty earlier in the game.
"(It) was a clear red card, I’m afraid to say," said Klopp, whose side moved up to second place.
Newcastle manager Benitez, however, was not convinced.
“Watching from the bench, maybe," said Benitez. "Watching the reply, it was not very clear.
"The referee maybe had the same opinion, that it wasn’t very clear. Watching the replay, both situations was not very clear."
Had Lascelles been sent off, he would have missed Saturday's home game against Southampton.
Newcastle remain two points clear of the Premier League's relegation zone.
"We were playing against a dangerous team," said Benitez. "We know they have the pace up front. We managed to 40 minutes then it was a mistake.
"We had to go for it in the second half and were then more open. You have to keep the balance to be stronger in the defence and create chances in attack.
"We are learning, but we are still making mistakes against teams. We are improving, but this team has to get points."