The Saints’ defender made his England debut last month at the age of 18 and has been linked with a move away from St Mary’s this summer.
Shaw signed a new contract with the south-coast club earlier this season but still Manchester United, Chelsea and Arsenal are set to make moves for him in the summer.
However Pochettino believes Shaw could play for the best team in the world already and become the best left back on the planet.
“He can play at Real Madrid or he can play in the world starting XI,” he said.
“He really has the quality to do so. I am not sure if he is one [of the best left-backs in the world] already. I think so.
“I am not sure if he is already the best one in the world.”