Coulson joins the O`s to aid his recovery after spending the second half of last season out of action through injury.
The 28-year old, who has recently celebrated his testimonial with the U’s as a result of ten years’ service to the club, will switch to the Matchroom Stadium until January.
Coulson, who enjoyed a testimonial match against Tottenham Hotspur earlier this month, has played more than 260 times for United since making his debut against Halifax Town in 2007.
He featured prominently during the U’s Conference (National League) Promotion Final and FA Trophy winning season in 2013/14, before scoring the club’s first goal back in the Football League against Plymouth Argyle.
However, Coulson featured just a dozen times last season with a serious ankle injury sustained in the League Two fixture against Wycombe Wanderers, ending his campaign prematurely in November 2016.