The former Bristol City, West Ham United and Cardiff City striker spent a lengthy period on trial with Nottingham Forest in the summer.
Manager Dougie Freedman decided against offering him a contract, with the transfer embargo placed on the Reds meaning every spare place in Freedman’s squad was precious.
Maynard then signed a deal with the Dons in September with manager Karl Robinson telling his official club website at the time: "With Nicky we were firm from the word go with what we could offer and initially it was a shock for him and his people.
"They had to go away and think about it but I'm delighted he's decided to sign."
Maynard netted for Milton Keynes in Tuesday night’s vital victory against Sheffield Wednesday, a win that moved them out of the Championship relegation zone.
Meanwhile, Paul Williams has been appointed as first-team coach at the City Ground having recently been part of the backroom team at Brentford.