London - Scotland centre Alex Dunbar will be sidelined for up to nine months after rupturing the anterior cruciate ligament in his knee, the Scottish Rugby Union (SRU) have announced on Thursday.
The 24-year-old Glasgow player sustained the injury during training as Scotland prepared for their Six Nations encounter with England at Twickenham on Saturday, in which he was due to start.
A subsequent hospital scan revealed the extent of the damage, ruling Dunbar out of the rest of the season and seriously jeopardising his chances of competing in this year's World Cup in England, which starts in September.
Speaking before the extent of Dunbar's injury had been confirmed, Scotland head coach Vern Cotter said: "Alex was in a bit of discomfort. He just went down on his own. It was a change of direction and then he went down.
"It's very unfortunate and he's obviously upset. He will miss this Calcutta Cup game and we're hoping it's only a minor injury. We will have to wait and see.
"My worst fear is that it could be an ACL (anterior cruciate ligament). Hopefully it's not. If it is an ACL, it will be a fine cut (for the World Cup).
"But they are pretty good at getting these types of injuries back, if that is the case. It's not as severe as it used to be, but certainly it would be a setback for Alex."
Matt Scott has stepped in for Dunbar for Saturday's match at Twickenham.
In a statement, the SRU said: "The Scotland medical team today (Thursday) confirmed that Glasgow Warriors centre Alex Dunbar is out for the rest of the season through injury.
"Dunbar was set to start for the national team against England in this Saturday's Calcutta Cup clash at Twickenham when he injured his knee a few hours before the team's departure from BT Murrayfield.
"A scan at Spire Murrayfield Hospital later in the morning revealed he has ruptured his ACL -- anterior cruciate ligament -- requiring surgery and around six to nine months rest and rehabilitation."