The Uruguayan striker was expected to find his best form with the Reds by this season.
However, he has failed to take the chances given to him by manager Arne Slot.
Nunez did not score in a 1-0 win over Girona in the Champions League and is now five games without a goal.
“It’s the story with Darwin Nunez,” said Garcia on ESPN FC’s YouTube channel.
“We all agree - his work rate is fantastic. He’s helping the team because he’s always trying to push the opponent but we’re missing the last part - the scoring rate.
“It’s something we’ve been waiting for for the past years but it’s not arriving. He can score goals but he’s not a player who can maybe score 25-30 goals.
“Something is missing there and we’re still waiting. Every single game he gets one, two, or three chances and he’s missing the last part.
“He’s missing a little bit of composure in the last moment.”