However, the Reds were saved against Girona by talisman Mohamed Salah, who scored a milestone Champions League goal in a 1-0 win for Arne Slot's side.
During the first half, Nunez ran into a dangerous position in the area as a high cross was sent in from the right.
The Uruguayan had a great chance to head the ball towards goal or his onrushing teammates, but his effort was lacking.
Nunez merely glanced at the ball and it bounced into the path of Girona defenders before they cleared their lines.
Former Watford striker Deeney, who was on commentary for talkSPORT, couldn't believe what he saw from the Reds star.
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"Darwin Nunez, what are you doing?" he asked. "He's headed that with his eyebrow! Every time he goes through one-on-one I don't think he's going to score.
"He doesn't look like he's going to score, he looks like he's just hitting it and hoping."
Nunez was played through into the box moments later but his shot was saved by former Tottenham goalkeeper Paulo Gazzaniga.
Liverpool and Girona went into the break at 0-0, though the match-winning goal came shortly after the hour mark in the second half.
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Donny van de Beek was adjudged to have stood on the heel of Luis Diaz and, after a lengthy VAR check, a penalty was awarded.
Salah was the man trusted from 12 yards and he scored for Liverpool, with the goal being his 50th in the Champions League.
The Egyptian's latest strike has seen him go joint-tenth in the all-time standings with the legendary AC Milan striker Filippo Inzaghi.
He has also overtaken Zlatan Ibrahimovic, Alfredo Di Stefano and Kylian Mbappe, as well as extended his season goal tally to 16.
In addition to this, Salah is one goal away from equalling Billy Lidell's record of 228 goals for Liverpool.
The Reds held onto their one-goal lead to maintain their 100 per cent record in the Champions League and stay top of the table.
Arne Slot's side, who have conceded just once, are all-but through to the last 16 of the competition.