Spurs lost talisman Harry Kane to injury early on, but did not let it knock them out of their stride and made short work of the League One outfit, who were hoping to cause a shock.
Tottenham Hotspur's 6-0 FA Cup win over Millwall was a bit of a pyrrhic one for Spurs after Harry Kane went down holding his ankle in the first half.
Tottenham is second in the standings but it will now be sweating on the results of the medical scans on Kane's right ankle.
Speaking aftwerwards Tottenham manager Maurico Pochettino said: "It's the same ankle as before in the Sunderland game".
"I am sure it will be left to the authorities", Harris said.
Despite the striker's absence Tottenham netted six goals against The Lions, with Son Heung-min scoring his first hat-trick for Spurs while Dele Alli, Christian Eriksen and Vincent Janssen also all found the back of the net.
Pochettino admitted later to major concerns about Kane, who looks certain to miss England's games against Lithuania and Germany later this month. We can not cry. We have enough players to replace him and win games.
Kane has scored 19 times and set up four more in just 22 Premier League games this season, and when he is on target, Spurs usually win.
"It is another London derby and we were watching all the games and they fully deserve to be in the quarter-finals".
"Son can play like a striker", Pochettino said. "Me personally, but also the club, we will not condone that, if there is [proof]".
"Of course it's a shame, for both of us - Mauricio wants to be talking about his team's quality".
Leicester complained to the FA about "abuse, provocation and intimidation" of their players fans and staff in their fifth round defeat to Millwall.
"We've enjoyed this competition - its' a been a great distraction for us", Harris enthused. "It's wrong in society and it's wrong in football". "Not only him (Janssen) but different players too will have the opportunity to play more and they need to be ready".
"Players like Vincent and Son, who haven't played in the last few weeks in the starting XI, may now be important for us".
"We know he's had some hard months although, of course, he's scored some penalties, but to [see him] score in open play today was a good feeling".