#3 Manchester United
Manchester United were one of the most disappointing clubs in 2020 and struggled with inconsistency throughout the year.
The Red Devils have very much been a Jekyll-and-Hyde club under the management of Ole Gunnar Solskjaer, and nowhere was this more evident than in 2020.
Positive results were registered against the biggest sides in the league but they were usually followed with disappointing results against lower sides.
In many ways, it was a case of one step forward, two steps backwards for Manchester United. Proof of this lies in the fact that they qualified for three semi-finals in 2020 but failed to progress to any final.
Their Champions League group stage elimination after winning their first two games against Paris Saint-Germain and RB Leipzig proved to be the nadir of the year.
Having said that, there are positive signs for Manchester United to build on heading into 2021.
#2 Manchester City
Unlike all the other clubs on this list, Manchester City ended 2020 with a trophy in the bag, as they continued their recent dominance of the League Cup with an emphatic victory over Aston Villa in the final.
However, with all due respect to England's third competition, the Cityzens have their sights set much higher but failed to make a mark on the competitions where their ambitions really lie.
Their Premier League title was effectively surrendered to Liverpool by Christmas, while an unfancied Arsenal ended their FA Cup charge in the semi-final stage.
Their most disappointing result, however, came in the quarter-final of the Champions League where a 3-1 defeat to Olympique Lyon meant that the Mancunians have still not made it to the last four on the continent under Pep Guardiola.
This was a far cry from the heights that saw the club become the first team in English football history to win a domestic treble the year before.
The new season has not started too brightly either. City have struggled to get going in the current campaign and currently sit 6th on the Premier League table, with the goal-shy side having scored just 21 goals from 14 league games.
#1 Barcelona
The year 2020 was generally one to forget for Barcelona, and they were undeniably one of the most disappointing clubs of the year.
It started brightly enough for the Catalans but a 3-2 defeat to Atletico Madrid in the semi-final of the Spanish Super Cup in January proved to be the catalyst for the domino effect that followed.
Erstwhile manager Ernesto Valverde was relieved of his duties and was promptly replaced with Quique Setien. The former Real Betis manager himself lasted less than seven months on the job.
When La Liga joined the rest of the world in shutting down in March 2020, Barcelona had a two-point advantage at the summit of the table and were primed to retain their title.
However, a spectacular capitulation post-lockdown saw them end the season five points behind bitter rivals Real Madrid.
However, the worst was yet to come as a total annihilation awaited them in the Champions League where Bayern Munich trashed them in an 8-2 defeat.
This was followed by the sack of Quique Setien and the appointment of Ronald Koeman. However, the biggest setback Barcelona suffered was when Lionel Messi submitted an official request to leave the club.
The Argentine ace ultimately elected to stay at Camp Nou but Barcelona ended the year trophyless for the first time in 12 years, which was a disappointing end to one of the worst years in the club's illustrious history.