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Suarez, 34, left Barcelona last summer in a £5.5m deal to Atletico Madrid after Ronald Koeman told him he wasn't part of his plans at the Camp Nou.
But the Uruguayan striker's form hasn't dripped since leaving Barcelona as he has scored 16 times in 26 appearances across all competitions for Atletico this season.
Suarez is currently second in the La Liga goalscoring charts this season -- three behind former teammate Lionel Messi -- as Atletico mount a title challenge.
Forlan has argued that it was a "huge mistake" on Barcelona's part to cut ties with his fellow countryman.
When asked about the decision to sell Suarez, the former Manchester United player told AFP: "Of course it was a huge mistake.
"As soon as Barcelona said he was for sale, I knew it was a mistake. All I know is it wasn't about his performances on the pitch.
"I messaged him and said, 'Listen, you're not the first and you won't be the last. You have to keep being yourself. You don't have to prove anything to anyone so just keep doing it at Atletico Madrid.'
"But when you get punished for something you didn't do, when you're still in great shape, playing well, of course your aim is going to be to show that you can still perform."
Suarez was visibly upset after he ended his six-year stay at the Camp Nou amid growing tensions with Koeman and former Barcelona president Josep Bartomeu.
Barcelona's season has started to bounce back as they are back in the La Liga title race and have reached the Copa del Rey final.
However, the Spanish side have relied on Barcelona talisman Messi and missed the influence of Suarez in the final third.
Ronaldo's sensational exit from Madrid saw Los Blancos finish the following season in third place in La Liga and without any major silverware.
Madrid, who only won the Club World Cup in the 2018-19 season, also axed Julen Lopetegui and Santiago Solari before Zinedine Zidane returned as head coach.
Former Atletico star Forlan has now compared Barcelona's current inconsistencies without Suarez to those Madrid endured without Ronaldo.
"Barcelona are missing Luis, it's like when Cristiano Ronaldo left Real Madrid," he said.
"It was not just Cristiano Ronaldo leaving, one of the best players in the history of football. It is 50 goals leaving as well.
"So if you sell a player like Ronaldo or Suarez, you have to replace them with two players and then there's risk because they have to adapt.
"As soon as Cristiano left, it was never going to be easy for Real Madrid and for Barcelona now it's the same."
Featured Image Credit: PA
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