The 21-year-old will go straight into the Minstermen's squad for this weekend's double-header against Bristol Rovers and relegation rivals Plymouth.
Hartlepool-born Reed has yet to appear for Sunderland but has had loan spells at Brentford, Bradford and Leyton Orient and has this season made 10 appearances for Portsmouth while on loan at Fratton Park.
Reed could make his first appearance for Nigel Worthington's side at Rovers on Saturday, subject to Premier League ratification.
He is the fourth player drafted in on loan by Worthington since he replaced Gary Mills as boss earlier this month following the arrival of Sheffield Wednesday goalkeeper Arron Jameson, Ipswich midfielder Josh Carson and Sheffield United forward Richard Cresswell.
- Sports & Recreation
- Bristol Rovers
- Nigel Worthington