Constantine had three chances of winning and just about held off his first goal which was a 25 yard free kick.
The fact that United only scored four goals in December gave Constantine a distinct advantage.
Current qualifiers for goal of the season are previous monthly winners
August Jo Kuffour v Coventry
September Alex Russell v Tranmere
October Alex Russell v Peterborough United
November Tony Bedeau v Wrexham
December Leon Constantine v Brentford