Formerly a member of the Czech national under-21 side, Polák, alongside players like Petr Čech and Milan Baroš, was a part of the team which won the European Under-21 Football Championship in 2002.

[4] In 2005, he was transferred from the Czech First League team FC Slovan Liberec for a fee of €1,500,000 to the Bundesliga side 1.

In the same year he played for the first time under Czech national coach Karel Brückner.

The Czech international reportedly cost €3.5 million and was at the time the second most expensive transfer in Anderlecht's history, as well as one of the highest paid players in Belgian football.

He was Anderlecht's box-to-box midfielder playing a crucial role in their 2007–08 Jupiler League season and the 2007–08 UEFA Cup.