#3 Joe Gomez
After arriving from Charlton Athletic in the summer of 2015, Joe Gomez has had an injury-riddled stint at Liverpool.
Nevertheless, the 23-year-old centre-back has played a key role in the center of the Liverpool defence alongside Virgil Van Dijk. Gomez has made over 120 appearances in all competitions for the Anfield club and has featured in their triumphs in the Champions League and Premier League in the last two seasons.
However, Gomez suffered a knee injury while on international duty with England. An official statement by his club regarding Gomez's injury read:
"The issue was isolated to Gomez's tendon, with no damage to any other associated knee ligaments. No timescale is being placed upon his return, though the issue is likely to rule him out for a significant part of the remainder of 2020-21."
Gomez's absence is a significant blow to Liverpool manager Jurgen Klopp, as another center-back - Virgil Van Dijk (more on him later) - is already out of action with a long-term injury.
#2 Ansu Fati
Barcelona teenager Ansu Fati has already etched his name into the club's history books despite only turning 18 last month.
After bursting onto the scene last season, where Fati became the youngest scorer in the Champions League, the striker has seen more game-time under new Barcelona manager Ronald Koeman this season.
The teenage prodigy, who scored in Barcelona's home defeat in the El Clasico, has already netted five goals for the club this season. However, Barcelona received a huge blow when Fati tore the meniscus in his left knee in the club's La Liga win over Real Betis last weekend.
Fati, who has already made 43 appearances for the club in all competitions, has been successfully operated upon but is expected to be out of action for at least four months.
It is a huge blow for Barcelona at a time when have made an indifferent start to the season, and captain Lionel Messi is looking a pale shadow of his illustrious self. For now, Ronald Koeman and Barcelona have their hands full.
#1 Virgil Van Dijk
The Dutchman, widely regarded as one of the finest center-backs in the game at the moment, has been one of the key players under Jurgen Klopp's tutelage at Liverpool.
Such has been his importance to the Liverpool cause that Van Dijk played every league game for Liverpool in the last two seasons while helping the club win their first English top-flight title in three decades last season.
In the Anfield derby against Everton this season, Van Dijk damaged his knee ligaments following a challenge from Jordan Pickford.
The player has undergone a successful surgery but is ruled out for large swathes of the season as he faces a long rehabilitation period.
A club statement in this regard read:
"Van Dijk will now immediately focus on the beginning of his rehabilitation with the support of the Reds' medical department. No timeframe has been placed on the Dutchman’s return to action.”
Van Dijk's injury is a huge blow to Liverpool's hopes of successfully defending their Premier League title this season. An injury to Joe Gomez has further compounded Jurgen Klopp's in this regard.