Gomez, who played the full 90 minutes in Thursday's Europa League clash against Toulouse, suffered a minor knock, preventing him from recovering in time for the Brentford encounter.
Ibrahima Konate, although part of the squad, was left out of the starting line-up as a precaution.
"We will see how serious it is. But they are unavailable today, so that's the reason for the changes," the German told Sky Sports prior to the game.
"In this part of the season, a lot of teams struggle a bit with injuries. It's the same for us in the moment, so that's how it is and we have to deal with it, and we do that."
The absence of experienced players impacted Klopp's bench selection, with only Luis Diaz above the age of 20 among the substitutes.
In midfield, the Reds are struggling too. Alexis Mac Allister's one-game suspension added to the injury challenges (Curtis Jones and Ryan Gravenberch have knocks), pushing Klopp to call upon young players to make up the numbers in the 20-man squad.
In addition to Diaz and substitute keeper Caoimhin Kelleher, Trey Nyoni (16), Ben Doak (18), Luke Chambers, James McConnell (both 19), Harvey Elliott and Jarell Quansah (both 20) made up the rest of the bench for the Reds.