Alderweireld has been heavily linked with a move away from North London due to a lack of progress in talks over a new contract, while injuries have limited him to just one appearance since February on the field too.
The uncertainty over his future has forced Mauricio Pochettino to look for alternatives, and a £45m approach for Ajax defender De Ligt has reportedly been mooted.
The 18-year-old has already made 60 appearances for Ajax and won five caps for his country, becoming the Netherlands' youngest debutant since 1931 when he made his international bow.
Spurs could face competition for De Ligt, though, with North London rivals Arsenal and Spanish giants Barcelona having previously been credited with an interest in him.
Pochettino's side have also been linked with the likes of Alfie Mawson and Harry Maguire, but are thought to have made De Ligt their number one choice.