Pochettino was playing with Espanyol in the latter stages of his career when the club apparently explored a loan deal for Barca's Messi.
The Spurs boss was responding to comments from Brendan Rodgers after the former Liverpool manager claimed he came close to signing Dele Alli.
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Now at Tottenham, Alli is quickly emerging as a rising star of English football, but Pochettino does not see the value in talking about what might have been.
"Do you know how many players in football are close to signing for many clubs? It's only one comment from some manager. Dele Alli now is here," the Argentine said.
"We were close at Espanyol to signing Lionel Messi – a centimetre. Unbelievable but this was true.
"Messi was 17, playing for the Under-18s and very close to signing for Espanyol. It was close but it never happened.
"In football it's always 'if, if, if' but in football it's about reality. It's not about maybe what could have happened."
Alli scored one of the Premier League goals of the season so far as Tottenham beat Crystal Palace 3-1 away on Saturday, as the teenager flicked the ball over his head and turning before volleying into the>