SCOTLAND assistant coach Mike Blair has called on World Rugby to extend the length of the World Cup and increase the number of players who can travel to the tournament after admitting the current set-up leaves competing nations "vulnerable".

The Dark Blues face a make-or-break double header with Russia and Japan just four days apart as they seek to reach the quarter-finals.

The Scots need two wins and at least one bonus point - perhaps two depending on how they fare in their final game with the Brave Blossoms on October 13 - to seal qualification to the last eight.

But Blair is concerned the strain of playing two crucial matches in such quick succession will leave Gregor Townsend's squad - currently limited to 31 players - flagging after admitting some team members may be asked to put their bodies on the line in both clashes.

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It is too late to change the rules and schedule for this year's competition in the Far East but Blair says the situation should be looked at in future.

The former Scotland scrum-half said: "I think bigger World Cup squads would certainly help. It's a challenging position to be in.

"You leave yourselves a little bit vulnerable in some positions when you cut down to 31-men.

"So there's no doubt a couple more players would definitely help, as would potentially extending (the competition) an extra few days so everyone gets similar breaks in between.

"It's unique. It's not something that happens during the normal season. It's another challenge we've got to take on and to enjoy.

"We're looking at guys backing up. There might be guys who don't go on the pitch 100 per cent fit and that's something that might need to be looked at."

Vice-captain John Barclay should be available to face Russia next Wednesday after overcoming a groin strain while prop Allan Dell is working his way through concussion protocols after coming off early during Monday's bonus-point win over Samoa.

But Blair admits Townsend's back-room team will have to manage their numbers carefully.

"It's obviously a challenge," he said. "Russia first up that's what that focus is going to be on, but at the same time we are aware we've got that four-day turnaround straight after so how we look after the players, the volume of training we do, the direction in which we take training, what we focus on is going to be really important.

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"It should be seamless for the players, we don't want to add undue stress on to them in that period where they are going to have to recover quickly.

"Some guys will have to back up because of the numbers in the squad and the make-up of the squad we've got, so looking after them, preparing them to be able to perform from a physical point of view is going to be really important.

"A lot of teams have got it in this World Cup where there's a four or five-day turnaround. That's how the tournament was structured and we've known that for a long time so we've had that in our minds.

"It doesn't keep everyone on a level playing field but that's what happens, we'll deal with it. We are really confident in the ability of our guys to back-up."

Scotland's campaign got off to the worst possible start as they were humiliated by Ireland in their Pool A opener.

This week's 34-0 triumph over Samoa has averted a disastrous early exit for now but the Dark Blues will have to win three straight games in a single tournament for the first time since 1999 if they are to make the knock-out rounds.

Blair added: "We have obviously got a bit of momentum from the Samoa game there.

"You say there was pressure on us, but it was also a massive motivator. We can't afford to slip up, so that is going to be a huge driving force for the players."