Sabatini revealed Lamela's move to Spurs was influenced by the Italian club's decision not to sell to a league rival.
"It was a painful sale for all of us. At the beginning we didn't think we could sell Erik and we didn't want to," he said.
"Then some new factors came into play and as time went on we started to consider the eventuality. A club made him an offer that we didn't and couldn't match.
"Rather than trying to win a war that we probably wouldn't, we opted to sell.
"When that Italian club offered him 3.5m a season, as well as a 2m commission to his agent father, we knew we had lost the player.
"His people started pushing for a renewal and that is when I started moves to sell him.
"Had we begun negotiations sooner then we probably could have sold him for an even bigger fee."
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