The 19-year-old centre-half was watched by Tottenham, Arsenal and Manchester City at the New Den on Tuesday evening.
Spurs are on the hunt for a central defender after missing out on Gary Cahill in the summer transfer window.
Sebastien Bassong is sure to leave White Hart Lane in search of first-team football in the January window, and Ledley King's injury problems means he can't play more than twice a week.
And it would seem Spurs are already looking at defensive options as coaches Joe Jordan and Clive Allen were present on Tuesday night to examine Dunk's qualities at close quarters.
However, Spurs will face competition for the signature of the skyscraper defender from Arsenal, who had chief scout Steve Rowley running the rule over the prospect too.
Arsene Wenger's porous defence has concerned the Arsenal manager and he has dispatched his scouts on a global search for the solution.
Initial reports on the callow stopper had been impressive and Rowley will now begin to compile a more detailed dossier.
Manchester City are also monitoring Dunk's progress and had a scout of their own present to watch him in action against Millwall.
Gus Poyet would be disappointed to lose such a promising player in the January transfer window.
Dunk started the season alongside skipper Gordon Greer, following injuries to more senior defenders, and has blossomed beyond all recognition.