Barcelona La Masia staff remain frustrated over the club's failure to re-sign Takefuso Kubo.
Kubo had been with Barca since a junior before being forced to return to Japan as part of FIFA sanctions over their youth recruitment policy.
Kubo is already impressing Castilla coaches, convinced they've pulled off a transfer coup.
And a La Masia source told AS: "Kubo? This is the worst mistake of Barça for several years."
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