The 21-year-old has made another temporary move north of the border, after completing a successful spell at St Johnstone in the second half of last season.
He made 12 appearances for the St Johnstone and scored a header from a corner in a 4-1 defeat against Aberdeen at the end of March.
His stint at McDiarmid Park followed another loan spell at Dutch outfit FC Utrecht.
Willock, who joined United in 2012, has come through the ranks at the club and has represented both the Under-18s and Under-23s.
He has been named on the first-team bench on a couple of occasions and came close to his senior debut on the final day of the 2016/17 Premier League season, but Eric Bailly was able to soldier on after picking up an injury in the Reds’ 2-0 win over Crystal Palace at Old Trafford.