The Juventus defender appeared to press his boot into the back of the Spurs attacker's leg when he was on the ground.
The incident went unnoticed by the referee, but not by Tottenham fans who ripped into Barzagli on social media.
Tottenham legend Roberts also saw what happened, and the 58-year-old labelled it "disgusting".
Was disgusting— Graham Roberts (@GrahamRoberts4) March 7, 2018
The South Korean got his own back on Barzagli and Juventus prior to half time by opening the scoring for a goal that put the Lilywhites 3-2 ahead on aggregate as Maurircio Pochettino's side looked to be closing in on the quarter-final of the Champions League.
But a quickfire double from Gonzalo Higuain and Paulo Dybala midway through the second period flipped the game on its head and the Italian giants wound up progressing as 4-3 aggregate winners.