He made the comments after Arsenal's 1-0 home loss to Chelsea, and admitted he never thought he would have been suggesting the Gunners' bitter North London rivals as title contenders.
Spurs are only two points behind Arsenal, and Henry says it is no longer possible to discard Mauricio Pochettino's team as also rans.
He said: "Now, Tottenham, coming from nowhere, are two points behind Arsenal and nobody has been talking so much about them winning the title. Now, they are well in it. It's a four-team race for the title.
"They are in it. They are two points away from Man City and Arsenal with +22 goal difference. Arsenal have to go to the Lane. I never thought I would have said it, but they are in it."
Henry is not the only ex-Gooner who will be be feeling nervous right now. Former midfielder Paul Merson told SkySports last week that he will wear a Tottenham shirt on air if Spurs finish above Arsenal in the table. Seeing them lift the trophy would be a nightmare scenario.
Both teams could however miss out. Manchester City are level on points with Arsenal and lurking ominously, while surprise package Leicester City are top of the table and three points clear.