Academy prospect Sam Byrne is set for a lengthy spell of rehabilitation after suffering the injury.
Everton Under-21 prospect Sam Byrne is set for an extended spell on the sidelines after breaking in training in what academy manager David Unsworth called a "freak accident".
The 20-year-old striker joined the Toffees in 2014 after being released from Manchester United's youth academy but is yet to feature for the first team.
He has scored three goals in 15 appearances for the Under-21s side, but is now expected to be be ruled out for a considerable length of time.
Unsworth told the club's website: "It was a freak accident. The boys are all gutted for Sam because they are a close group and he’s a popular member of the squad.
"We will give him all the support he needs and I look forward to having him back amongst us as soon as possible."
Byrne has played senior first-team football at Carlisle United, having spent time on loan at Brunton Park from the Red Devils in 2013-14, where he scored once in 13 games.
The Republic of Ireland Under-21 international had recently scored in the Toffees' development squad's win over Southampton, and was finally beginning to put together some impressive form after seeing his first two years at the club truncated by injuries.
Named the FAI's Under-19 international player of the year in 2014, the youngster has been hotly tipped to have a bright future at both club and national level.