Dynamo on Tuesday posted a statement on their official website which said Buttner's contract was "agreed upon" and that only "technical details" were being settled, and which was accompanied by pictures of the left-back in their training kit.
The 25-year-old Dutchman said: "I want to play in the Champions League, win trophies.
"Dynamo are a very strong team and I am confident that we will fight for first place this season."
Buttner has made a total of only 28 appearances in all competitions, scoring two goals, since joining United from Vitesse Arnhem in the summer of 2012.
His fellow left-back Patrice Evra in May signed a new contract with the Red Devils, who have been linked with another player in that position, Southhampton's England international Luke Shaw.