The Dane was axed by Tottenham this week with immediate effect and has already banked his payout.
Danish media sources say Frank is instantly £8 million richer after less than eight months in the job.
Tottenham paid Brentford £10m to prise Frank away from the summer and secured him to a three-year contract.
He left Tottenham 16th in the Premier League and just five points above the relegation zone after a run of two wins in the last 17 matches.
Tottenham are now in talks with former Juventus coach Igor Tudor to take charge to the end of the season.