The centre-forward made headlines in the summer when he publicly stated his desire to leave Spurs, with Manchester City the team with the greatest interest in his signature.
However, Kane stayed at Spurs after the club refused to negotiate with City or any other English team, but he has struggled for form and goals so far this season.
Keane told ITV Sport after England's 1-1 draw at Wembley with Hungary: "There is no middle ground with Kane.
"When he's on fire he is fantastic and when he is off - and we've seen many times before - it's like he is on his heels and he can't get up to speed with the game.
"Whatever is going on at club level, he does need to do a bit more when he's not at his best in terms of general play."
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