The North London club signed the Croatian midfielder from Dinamo Zagreb in 2008, with rumblings of tax evasion.
The now Real Madrid midfielder was a big-money addition for the North London club, with the deep-lying playmaker going on to become an important player at White Hart Lane.
However, a number of Croatian television stations are reporting that police have got involved in investigating the deal, with Dinamo being accused of not paying tax on the signing.
HRT claim that Dinamo president Zdravko Mamic yesterday had documents removed from his house by authorities for investigation.
Modric was an influential member of the Tottenham team that qualified for the Champions League in 2011-12 and has since become a world-class player.
With Spurs failing to consistently qualify for Europe’s top tournament, they could no longer hold on to the central midfielder and were forced to sell the eastern European schemer to Real Madrid.
Since moving to the Santiago Bernabeu, Modric has become a key man for the Spanish giants and was sorely missed last season when he was absent for a prolonged period through injury.