Gregor Townsend confessed it "doesn't look good" for Hamish Watson after admitting the Scotland flanker's World Cup might be over already.
The Dark Blues suffered a 27-3 mauling from Ireland in Yokohama and there was further pain for Edinburgh forward Watson following an incident just before half-time.
He could be heard letting out a huge scream as his left knee appeared to buckle after being caught in a tangle with Irish props Cian Healy and Tadhg Furlong.
Watson left the field on a stretcher and will now be sent for a scan this evening.
But Townsend is already drawing up plans to promote Magnus Bradbury - who had already travelled to Japan on stand-by following an earlier facial injury to Jamie Ritchie - to his squad if his Edinburgh colleague is forced out of the tournament.
Townsend said: "Hamish is our only injury concern.
"He had a knee injury that we will be hopefully getting more information on tonight with a scan.
"It doesn't look good when a player is stretchered off the field, so hopefully we'll know more later tonight.
"It would be bad luck for any player if he misses the World Cup. We had Sam Skinner miss out on selection ahead of the World Cup.
"But we have always presumed that there will be people who will miss the World Cup after each game that we play. Let's hope that's not the case with Hamish.
"The good news is that Jamie Ritchie will be available for our next game after returning to full training.
"Magnus is obviously still here in Japan too. We held onto him just in case we didn't have any luck with injuries this weekend.
"So if Hamish was to miss out then Magnus would be the obvious choice to replace him."
Ireland celebrated a bonus-point win as James Ryan, Rory Best, Furlong and Andrew Conway all crossed over but it was a dismal start to the campaign for the Scots
Townsend was left to admit his team failed to turn up during the opening 25 minutes, allowing Joe Schmidt's men to put the game to bed with three quickfire scores.
But he backed his side to bounce back in eight days when they face Samoa in Kobe.
He said: "It was disappointing, we didn't start with the energy, accuracy or aggression required to beat a team like Ireland.
"They started very well and took their chances when they got into our 22.
"They're one of the best teams in world rugby and if you give them a 15 to 20 point start it's going to be very difficult to come back.
"They just converted mistakes into territory, mistakes into points directly.
"We need to win our next three games, whatever the result was today we needed to win the next three games.
"But I believe in this squad to bounce back and be much better against Samoa in eight days' time."