Forest chief executive Mark Arthur said: "This represents a great opportunity for both of them and we felt we could not stand in their way.
"Both players are understandably ambitious young men and are keen to play in the Premiership as soon as possible.
"The contributions of Andy and Michael to Nottingham Forest in recent years has been immense.
"They have been with us since they were schoolboys and have developed into two of the finest young players in the country.
"We will watch their progress in the Premiership with both a great deal of interest and pride.
"I would like to take this opportunity to thank them both for their efforts and wish them the best of luck for the future."