McKenna went off injured hours after fellow Scotland centre-back John Souttar was ruled out for the season after suffering an Achilles injury during Hearts' victory over Rangers.

The injury now makes McKenna a doubt for Scotland's Euro 2020 play-off semi-final against Israel on March 26.

McInnes said: "I don't know how significant it is. I don't know if he has overdone it in the gym, his back was a bit stiff on Thursday and he didn't train on Friday but we were confident he'd be fine.

"His back and hamstring were tight going into the game but it was his other hamstring that went.

"I don't know until Monday until we get him imaged and see what the damage is but I think it's some sort of tear of the hamstring.

"It depends on the grade of the tear. Hopefully he can get back for us before then and if he does he can be there for Scotland as well."

Aberdeen progressed to their ninth semi-final in seven seasons under McInnes after Lewis Ferguson sent them on their way with a sublime strike with the outside of the boot in the seventh minute.

There were very few more chances until substitute Sam Cosgrove netted a stoppage-time penalty.

McInnes said: "Fergie's goal was brilliant, real quality. I have been chipping away at him, he needs to do more of that.

"We have got more midfield options back in the team and it allows him to get further forward but when you see quality like that, he should be scoring more goals.

"We started the game excellent. St Mirren were the better side towards half-time. They had a lot of possession but didn't hurt us.

"We defended well second half but I was screaming to get ourselves up the pitch. Maybe the players felt subconsciously that 1-0 was enough but I wanted to get more of a focal point, which is why I brought big Sam on.

"With Sam applying pressure to centre-backs, we get our rewards with a penalty."

St Mirren boss Jim Goodwin was frustrated after his side failed to turn their superior possession into clear-cut chances – they only managed one shot on target.

"I thought we were the better team, played the better football," Goodwin said.

"The bottom line is the two goals we concede are extremely poor. The first one we drop a midfield runner, which is something we spoke about in the build-up.

"And the second goal, at that late stage of the game, it's stupid to be messing about on our 18-yard line.

"We were very good from back to middle. We lacked a wee bit of cutting edge. We didn't work Joe Lewis at all – he made one save in the second half from Jamie McGrath but it was quite straightforward.

"At the same time, Vaclav Hladky has had to pick the ball out of his net twice when he has had absolutely nothing to do either.

"I'm really frustrated. I felt my team were better but we just didn't do enough to win the game."