Real Madrid are known admirers of the Welsh wizard, with the Spanish giants' director of football Zinedine Zidane revealing he is a fan.
McManaman told The Sun: "He's 23 and still very young. It's a different scenario for Gareth (compared to me) - he's a new father and he has time on his side.
"It all depends on what he wants to do, whether he's comfortable in London or if he wants to play abroad.
"Sooner or later, he needs to be playing against the best people in the world.
"He needs to be testing himself against the best players in the world because he is arguably one of the best players in the world.
"Sooner rather than later, he'll want to be playing in the Champions League. Tottenham didn't deliver that so I think they'll struggle to hold onto him."