Liverpool defender Andrew Robertson slammed Dominik Szoboszlai's mistake in the FA Cup win over Barnsley as "unacceptable", admitting his side still have room for improvement despite their recent unbeaten run.
Szoboszlai was guilty of a careless blunder when his miscued back-heel inside his own penalty area allowed Barnsley's Adam Phillips to score in Monday's third round tie at Anfield.
Liverpool were leading by two goals at the time of Szoboszlai's miscued pass and went on to clinch a 4-1 win against their third-tier opponents.
Szoboszlai had scored a superb long-range opener earlier in the game, but Liverpool boss Arne Slot said he would speak to the Hungarian about what he called a "weird" decision.
Robertson was equally frustrated by Szoboszlai's needlessly casual error, which led Barnsley manager Conor Hourihane to accuse Szoboszlai of disrespect.
"The frustrating thing is Dom does this unbelievable 60-yard sprint to start with, he's getting the clap off The Kop and I don't know if that maybe went to his head," Robertson said.
"We can joke about it now but it's unacceptable to lose a goal like that. Dom obviously knows that. He's been magnificent for us this season and he was again really good.
"He just had a lapse of concentration, and we can't afford too many of them in the six-yard box."
Liverpool have extended their unbeaten run to 11 matches to ease the crisis that engulfed the Premier League champions earlier this season.
But Scotland left-back Robertson said the Barnsley game provided further evidence that Liverpool still have a dangerous habit of letting teams back into games.
"Going 11 unbeaten is good but some of the performances still have to be better. Everyone knows that," Robertson said.
"We've looked a bit more secure defensively which is pleasing but now we need to put it all together because people are saying we're lacking an attacking threat.
"If you want to win trophies and go further in tournaments, you have to get the perfect balance. That's what we're working towards."