He said: "I've just not got the heart for it any more and I don't see the point in going through the motions.
"I've had a lot of knockbacks in my time but this has nothing to do with injury.
"I just don't enjoy it anymore."
For years, and years, and years, Tottenham Hotspur Football Club have fought tooth and nail to become a Champions League
Manchester United host PSV in the Champions League on Wednesday.
Juventus midfielder Claudio Marchisio is wary of a potential Manchester City backlash in Turin this week.
Michel Platini and Sepp Blatter could be facing lifetime bans from football if corruption charges against the pair are proven.
Arsenal are looking to reach the knock-out stage of the Champions League for the 13th season in a row.