Standing, 26, has been offered a trial by boss Jim Smith and he played in the second half of Saturday's pre-season friendly at Didcot Town, which United won 3-1.
Standing is a still a free agent since leaving us in May 2006. He has had trials and non-contract spells at AFC Bournemouth, Chesterfield and QPR but has yet to seal a contract.
However, a stumbling block could be the Blue Square Premier wage cap rule.
Smith said last week that should Mickey Corcoran sign a deal then that would be it for new players. But to complicate matters the Irishman has yet to take up the offer of a contract.
Although Smith who admitted that he wanted to sign Standing, said a player would have to be off-loaded to make room.