Daniel Stendel claims his contract was terminated immediately when he left his role as head coach of Championship club Barnsley in October.
The 45-year-old also said he was given no detailed reason for his dismissal.
Stendel begins life as Hearts boss on Tuesday with Barnsley seeking a claim for compensation against Hearts.
Hearts say Barnsley's case is "completely without merit" and that they followed "all proper procedures" over Stendel's appointment.
The German starts a two-and-a-half year deal at Tynecastle just over two months since his departure from Oakwell.
Stendel led Barnsley to promotion from League One in his first season in English football but departed in early October after a run of no win in 10 Championship matches.
"During my entire time at Barnsley, I gave my full commitment, energy and passion for the club and their supporters," he said in a statement on his Facebook page.
"The start to this season was very difficult though, but I always remained committed and accepted all the decisions of the board.
"This including the decision to terminate my contract with immediate effect. At the day of my dismissal, I wasn't informed about any detailed reasons."
On Monday, Barnsley issued their own statement in which they claimed they had been attempting to negotiate settlements for the services of Stendel and coaches Dale Tonge and Chris Stern.
They also claimed earlier this season Stendel had "entered into negotiations with a rival Championship club to take over their managerial post".
Stendel's own statement did not deny this had occurred and Barnsley say his decision to do so without board approval was "a clear violation of his contract".
"This event, coupled with numerous other issues, led to removal of Mr Stendel as head coach," the club said.