Scotland's World Cup plans have been dealt with a blow after it was confirmed lock Grant Gilchrist would miss the rest of the tournament with a groin injury.

And head coach Vern Cotter is still sweating on the fitness of influential playmaker Finn Russell ahead of next Saturday's crucial Pool B clash with South Africa after he was carried off during the Scots' 39-16 win over the United States on Sunday.

Gilchrist lasted just 18 minutes of the match at Elland Road and is now returning home. The Scottish Rugby Union say his replacement will be announced in due course.

An SRU statement said: "Scotland second-row Grant Gilchrist has been ruled out of the national team's Rugby World Cup 2015 campaign with a groin injury. "Gilchrist sustained the soft tissue damage in the 19th minute of the national team's 39-16 win over USA yesterday, with the recovery period expected to extend beyond the competition."

This is just the latest injury setback to beset Gilchrist, 25. The Edinburgh forward was due to skipper the Dark Blues during last year's autumn Tests but just a week after being appointed suffered an arm injury playing in a European Challenge Cup match in France that ruled him out for nine months.

The Scots have plenty of strength in depth in the second row, with Richie Gray, Jonny Gray and Tim Swinson already in the squad. However, Jim Hamilton, who would have been one of Cotter's likely first reserves, announced his international retirement after missing out on the original 31-man squad selected for England 2015.

What will worry Cotter more is the knock picked up by Russell.

The Glasgow stand-off has proven to be the Scots' talisman with his inventive style of play.

Grant Gilchrist© Steve Bardens - World Rugby/World Rugby via Getty Images

Duncan Weir replaced Russell after he was injured in the 60th minute against the States and scored the fifth and final try but Cotter will hope to have his first-choice 10 fit to face the Boks in Newcastle this weekend as they look to clinch a quarter-final slot.

The SRU statement added: "Finn Russell has sustained an inversion injury to his ankle, which will require further care and assessment.

"A number of other players will require the ongoing care of the national medical team however these are not considered an immediate concern."