Winlaton-born Greenwood has been at Sunderland’s academy since the age of eight and has progressed through every age group of the club’s youth system.
The 22-year-old signed professional terms in 2013 and renewed his contract in 2016 after an impressive season for the under-23s.
In February 2016, Greenwood’s performances saw him named the Premier League 2 Player of the Month, which led to him making his first-team debut under Sam Allardyce.
Greenwood started against Watford in May 2016 but has not made another senior appearance since.
A tricky winger with a rapid turn of pace, Greenwood has previously been called up to the England under-20 squad and has reportedly been the interest of a number of EFL clubs.
However, with first-team opportunities limited, his contract was cancelled this week and Gateshead were quick to snap him up with a half-season deal at the International Stadium.