Spurs' 3-1 loss to Arsenal in the north London has raised huge concerns about manager Nuno Espirito Santo, who was appointed in the summer, with the side playing poorly even in wins over Wolves and Watford.
The defeat to their fierce rivals, on the back of consecutive 3-0 losses to Crystal Palace and Chelsea in the league, has fans furious.
A 'non-existent' midfield has seen insipid displays with little to no creativity, coupled hasn't helped, while superstar Kane is yet to score in the Premier League this season.
And Allen feels the England capatain is low on confidence, as shown by one of his misses against the Gunners as Spurs pushed for a consolation goal.
"Harry Kane is a shadow of himself, there is no doubt about it," he told talkSPORT Breakfast. "The example of that from me was the chance that he had on the throughball, which he controlled brilliantly and then he lobs it over the keeper but lobs it wide.
"A Harry Kane that is confident in-form and is confident lobs that over the goalkeeper and it's in the back of the net. He's been affected. I don"t think anyone can arge that he's been affected by the situation and what was going to happen in the summer. Was he moving, was he staying?
But Allen insists the player IS dedicated to the club, despite his tumultuous summer.
he continued: "He is staying, I think he's totally committed to Spurs, there is absolutely no doubt about that, for me. Knowing Harry Kane, he's approaching it in exactly the same way that he did when he was in full flow."
Speaking about the display Tottenham put in against Arsenal, Allen sounded worried.
He added: "I think the alarming thing is that the performance in the opening game of the season against Manchester City was exceptional. The team showed exactly what it was capable of. The intensity, the way they went about the game and the problems they caused Man City.
"All of a sudden, since then they have dropped off, and dropped off alarmingly.
"Yes, Arsenal played well, there was no doubt about that in the first 45 minutes but Tottenham's shape and the way that they played, the lack of intensity was pretty alarming.
He added: "There are defensive frailities, we're letting in goals. And at the moment we can't score. Only scored four and conceded nine - that is worrying."
And Allen, who was once a coach at the club, agreed with former Spurs ace Jamie O'Hara that Nuno's team selection was part of the problem and praised one player for his second half impact.
He said: "Just look at the performance, the two halves, the first half performance, as we saw, the midfield was non-existent in terms of shape, in terms of being competitive.
"Oli Skipp came in and he did what he does well, that's exactly what you're asking from any player, especially in a derby game.
"Inevitably you don't play particularly well but you want to get the job done and you don't want to get beaten. Unfortunately that wasn't the case with Spurs."