Hughes was fired on Saturday, with the Abu Dhabi-owned club immediately appointing Italian Roberto Mancini in his place.
"I was informed after yesterday's match against Sunderland that my contract with Manchester City was being terminated with immediate effect," Hughes said in a statement issued through the League Managers Association.
"Notwithstanding media coverage to the contrary, I was given no forewarning as to the club's decision.
"Given the speed with which my successor's appointment was announced, it would appear that the club had made its decision some considerable time ago."
City have lost only twice in the Premier League this season but also won only two of their last 11 league games and Hughes said he was disappointed not to be able to see through his plans at what is now the world's wealthiest club.
"At the beginning of the season I sat down with the owners and it was agreed that a realistic target for the season would be sixth place (in the Premier League), or in the region of 70 points," he said.
"All of this was communicated to the players and we all knew where we stood.
"Whilst everyone at the club would obviously have wanted to see more wins, we were absolutely on target at the time of my dismissal. Only recently we had terrific victories against both Arsenal and Chelsea."
City are sixth in the Premier League and still in the hunt for a top-four finish and a place in the Champions League. They are also in the League Cup semi-finals, where they will play Manchester United over two legs.
"I am very proud of the fact that I steered the club through the most significant period of change in its history," said Hughes, who was appointed in 2008.
"I have always been aware of the responsibility that comes with being afforded the luxury of a significant transfer budget and I was grateful that the club supported me with significant investment in players.
"I very much regret, however, that I will not now be able to enjoy the success that would undoubtedly have followed in the light of that investment."
