Armstrong will self-isolate for 10 days from the date of the test – Tuesday, 6 October – and will now be unavailable for the game against Israel and the Nations League matches against Slovakia and Czech Republic.

All other members of the squad have returned negative results but due to being close contacts, Kieran Tierney and Ryan Christie – along with one physiotherapist and one masseur – will require to self-isolate for 14 days as of Tuesday, and will also miss the three matches.

Defenders Scott McKenna and Liam Palmer and attacker Oliver Burke will also miss all three games through injury leaving Clarke to come up with another way to get past Israel and into the final away to either Serbia or Norway.

He said: “I have some difficult decisions to make, some other decisions to make in terms of team selection which really is my main focus now.

“Hopefully everyone involved will come through with no issues, the health of anybody is more important than any game of football.

“I have now spoken to all three players involved in the situation, they are very disappointed not to be involved in such a big game. Everyone else has had a negative test.

“Now as the national manager I have to make sure we get the team on the pitch in the right frame of mind and ready to go for a positive result.

“We were working towards one team and now we have to change that. We moved the training back to this afternoon. We have a little bit of time to work on one or two different things, one or two different players coming into the team that maybe didn’t expect to play.

“Although it is disappointing for the ones who have had to drop out because of the situation, the ones who are going to get a chance to play – what an opportunity.

“I am not really one for big speeches. I trust my players, their mentality and attitude to get it right on these big occasions.

“Rather than a big Braveheart speech it will be calm, measured words to try and help them get through the game and get the right result for the country.”

Clarke is not surprised that the Scotland camp has been affected by the virus and will brace himself for similar situations in the future.

The former West Brom and Kilmarnock boss said: “If you look at the way the virus is spreading it is obviously becoming more prevalent as restrictions were eased, as everyone expected.

“There is no reason why it can’t infiltrate a football camp, no matter how secure your bubble and protocols are. It is something that is there, it is in everyone’s lives now, we have to adapt as much as we can and be prepared for. I tell the players that they have to be ready to step in at any time because we need everybody.”

If Scotland get past Israel they have the chance to reach the finals of a major tournament for the first time since 1998.

Clarke said: “Professional players know when they are taking part in a big game. Since we came into this camp there has been a little edge. I know the players are ready. Obviously today will be a down for them but come tomorrow night they will be ready for the game.”

As well as the three international fixtures, Arsenal defender Tierney will also miss his club’s Premier League clash with Manchester City on Saturday, October 17 as his self-isolation is due to end three days later.

He said in a statement on Arsenal’s website: “I’m so disappointed and frustrated to be in this situation.

“I have adhered to all regulations and made sure I was socially distancing from my team-mates in the hotel.

“I’ve also tested negative. I know Arsenal and the SFA are now in discussions with the Scottish authorities to gain a further understanding.”