The player is not the only Manchester United prospect to secure a loan move north of the border this January.
It has been reported that Tommy Wright is close to finalising a deal to bring the 21-year-old to McDiarmid Park, with United having recalled the midfielder from his original loan to allow the move to Scotland to go through according to The Sun.
Willock is yet to make his senior United debut, however, he has spent the first half of this season on loan in the Eredivisie with FC Utrecht.
He has made five appearances for the first-team and five for the reserve side in the Erste Divisie, Holland's second highest tier of professional football.
Willock will be hoping to make a similar impact in Scotland to that of his United teammate Demetri Mitchell.
Mitchell secured a loan to Hearts earlier on this month and the full-back has been extremely impressive so far in the games he has played.
In fact, if the deal goes through, Willock could find himself making his debut against his Old Trafford teammate, with the Saints due to play Hearts this weekend.
St Johnstone currently sit eighth in the table after 22 games, level on points with seventh-placed Kilmarnock.