Tokyo - Scotland flanker Hamish Watson has been ruled out of the Rugby World Cup after suffering a knee injury, further compounding the misery for the Scots who were disappointing in their opening loss against Ireland.

Coach Gregor Townsend has called up Edinburgh back-row Magnus Bradbury, who was already in Japan as injury cover, to replace Watson in the 31-man squad.

The news came as little surprise after Watson had to be stretchered off the field clearly in a huge amount of pain. A post-match scan revealed he could take no further part in the tournament, the Scotland camp said in a statement.

"While there is a high probability of picking up injuries during a Rugby World Cup, it is always disappointing to see someone having to head home," said Townsend.

"We feel for Hamish, who had worked so hard for this opportunity, and wish him well in his recovery."

The Scots came into the Rugby World Cup full of optimism and hoped to turn over Six Nations rivals Ireland in their opening Pool A clash, with the Irish back line missing three star players.

But Scotland were poor on a wet night in Yokohama and ran out 27-3 losers.

A disconsolate Townsend said his team must get "much, much better" and quickly if they are to progress in a pool that also includes hosts Japan and the dangerous Samoa.