The 22-year-old versatile midfielder has played 14 matches for the Ladbrokes Premiership side.
A major statement from St Mirren read: “St Mirren Football Club can confirm that Matty Willock has left the Buddies and will return to his parent club, Manchester United.
“The club would like to thank Matty for his contributions and wish him well for his future career.”
Meanwhile, Italian Serie A giant Juventus are allegedly keen on securing the services of the Red Devils striker Romelu Lukaku.
The Belgium international forward was not involved in Uniteds 5-1 win over Welsh side Cardiff City in the English Premier League last Saturday, with the striker handed compassionate leave by interim Manchester United boss Ole Gunnar Solskjær.
The former Chelsea and Real Madrid forward score 27 goals across all competitions for the Red Devils last season, but has managed only six goals in 22 games for Manchester United this season.
According to Italian publication Calciomercato, Serie A giant Juventus are keen on securing the signature of Lukaku, with the Turin giant viewing the 25-year-old Belgian as a player capable enough to lead them to the UEFA Champions League glory.
Earlier in the season, Romelu Lukaku, who has been heavily criticised for some below expectation displays this term disclosed that he would be interested in a mocve to Italy.
The 20-time English champions last week named former striker Ole Gunnar Solskjær interim boss until summer following the sacking of Jose Mourinho.