"Unfortunately team performance and results have not met the required standards, particularly this season despite a refresh of performance management strategies and structure at the end of last year and a significant change to the playing roster," said Doust.
"Whilst we can never predict the future the board determined that change was required for the balance of the 2014 season."
The club will begin the search for a new head coach for next season and beyond immediately.
McGregor said it was a difficult time and situation for everyone at the Dragons.
"The board wanted the change to be as simple as possible for the players and for their sake I agreed," said McGregor, a former captain of the team.
"This is a difficult situation for me.
"Steve Price is a good friend of mine and we have worked closely together and I would have liked us to work through these tough times as one.
"This change will be a new challenge for the players to face but we have a good football team and good group of men."
The Dragons face South Sydney next Monday night under their new coach. Doust praised the contribution of Price, who took over when Wayne Bennett departed for Newcastle after 2011, having delivered the joint venture a long-sought premiership in 2010.
"Steve Price has been involved at our club for over 13 years," said Doust. "He is a person of the highest integrity who has contributed enormously to our club in so many ways throughout this time."
- AAP
