The Red Devils acknowledged the allegations earlier on Sunday, but insisted that they would not make any further comment "until the facts have been established".
The 20-time English champions have now released a follow-up statement confirming that Greenwood will not take part in training or be considered for matches while the matter is ongoing.
"Mason Greenwood will not return to training or play matches until further notice," read a statement from the club.
Greenwood has scored 35 goals in 129 appearances for Manchester United, most recently playing in the 1-0 win over West Ham United on January 22.
The striker, who is yet to publicly address the allegations, has also played once for England, in a Nations League match against Iceland in 2020. body check tags ::