The Al-Hasawi family assumed control of the npower Championship club on Tuesday - and just 48 hours later they sacked Cotterill, who had been in charge for nine months.
In a statement via the League Managers' Association, the 47-year-old said: "I am deeply disappointed that I will no longer have the opportunity to manage Nottingham Forest Football Club and lead the team into this new era."
He added: "I thoroughly enjoyed my time in charge at the City Ground. Last season, after taking charge in difficult circumstances, I was proud to guide Forest clear of relegation and ultimately bring back some stability to the club.
"I fully appreciate that in football a change of ownership can unfortunately lead to a change of manager. Despite this, I believed the team's performances last season were good enough for me to be given a chance with the new regime and continue to build again for the new season.
"Nevertheless, I wish the club every success for the future. I would also like to thank my staff, players and the supporters. I enjoyed a fantastic relationship with every one of them during my time in charge.
"The matter of my dismissal is now in the hands of the LMA and I will therefore be making no further comment at this stage."
Cotterill's assistant Rob Kelly is in temporary charge of the first team while Glenn Hoddle has emerged as one of the favourites to take over along with former Forest star Roy Keane.