Brass, 37, followed former Scunthorpe manager Alan Knill to the club in March 2011 having worked as his number two at Bury. Knill was sacked in October and replaced by Brian Laws, who brought Russ Wilcox with him to work as one of his assistants.
"United can confirm that Chris Brass has left the club with immediate effect," read a short statement on the club's official website.
"The difficult decision was taken to reduce costs going forward as the club cannot sustain two assistant managers long term.
"The club would like to place on record its appreciation for all the hard work Chris has put in during his time with the club and wish him well for the future."
Brass made his name as a defender during an eight-year spell with Burnley and later went on to make over 150 appearances for York before ending his league playing career at Bury.