Scotland suffered a major blow on Monday when key flanker Hamish Watson was ruled out of the Rugby World Cup with a knee injury.

The 27-year-old, who plays his club rugby for Edinburgh, went down after a tackle in the first half of his team's 27-3 defeat to Ireland on Sunday and was immediately stretchered off the pitch at International Stadium Yokohama.

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

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

According to Scotland Rugby's website, Magnus Bradbury will replace his Edinburgh back-row teammate in the squad, with the 24-year-old already in Japan with the team as injury cover.

The injury comes at a difficult time for Scotland, with the team needing to right the ship after the heavy loss to Ireland. They next play Samoa on Sept. 30 before meeting Russia.

Scotland takes on Japan in the final pool-phase game of the tournament, a match that may determine which team escapes Pool A with Ireland.

In other injury news, South Africa prop Trevor Nyakane has also been ruled out of the tournament with a calf complaint.

He will be replaced in the Springboks' squad by Thomas du Toit.