Martial picked up the problem in United’s final Premier League game of the season.
Manchester United forward Anthony Martial has been ruled out of Saturday's FA Cup final against Manchester City due to a hamstring injury.
Martial picked up the problem in United's final Premier League game of the season in Sunday's game against Fulham.
Scans have revealed the full extent of the damage.
In a statement United said: "Anthony Martial is out of Saturday's Emirates FA Cup final against Manchester City due to injury.
"The France international strained his hamstring towards the end of Sunday's 2-1 win against Fulham at Old Trafford.
"Assessments have since revealed a muscle tear that rules the 27-year-old out of the Wembley showdown."
Martial missed United’s first two Premier League games this season due to a hamstring problem, while other small injuries since have restricted him to 29 appearances in all competitions in which he has scored nine goals.