The 30-year-old didn't make MK Dons' list of retained players as a number of the squad were cut following their relegation to League Two.
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The midfielder will now be on the lookout for a new club having previously been seen as the heir to Frank Lampard at Stamford Bridge.
McEachran graduated from the team's academy in 2010 and earned rave reviews all around, but spent the majority of his Chelsea career out on loan.
Spells at Swansea, Middlesbrough, Watford, Wigan and Vitesse made up most of his time at Chelsea, with the player joining Brentford on a permanent deal in 2015 after making just 22 first team appearances for the Blues.
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His former teammate Daniel Sturridge once told talkSPORT: "Josh McEachran is the future of Chelsea."
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Branislav Ivanovic was just as impressed, as the Serbian defender said in 2010: "I think all our young guys deserve their chances because they are really good.
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"I am really surprised with Josh McEachran because I have never seen a player that age in a team playing like him.
"I think, one day, we will be able to say we are happy because we will be able to say 'we played with him' because his performances have been amazing and if he keeps improving I think he can be one of the best players ever."
Chelsea's manager at the time, Carlo Ancelotti, was similarly effusive, and projected the youngster to replace Joe Cole.
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"Josh is not as quick as Cole, but he is a very skilful player," Ancelotti stated.
"He has to improve but he has a bright future. There are three or four players in the reserves and academy that could make the step up."
Ancelotti was clearly a big fan of the youngster, but when the Italian departed, his replacement Andre Villas-Boas wasn't so keen.
Upon returning to Stamford Bridge with Brentford in 2017, McEachran revealed how highly rated he was in Europe as a teenager.
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"Real Madrid and Manchester United came in when I was 16," he said.
"I could not believe it when my agent said 'Real Madrid want you'. Unbelievable, isn't it?
"Madrid had the contract waiting for me and they wanted all my family to fly over to sign a five-year contract, but I said, 'No, I want to stay at Chelsea'.
"I believed that I was going to make it [at Chelsea]. When I made my debut I thought, 'Ah, that was a good choice for me to say no to Real Madrid,' but looking back now maybe I should have [gone]."