Kobe - Scotland assistant coach Mike Blair has called for bigger Rugby World Cup squad sizes and a longer tournament in a bid to make teams less "vulnerable" to injuries and fatigue.

Competing nations are currently restricted to 31 players in their squads for the World Cup, which currently runs for just over six weeks.

Squad sizes and scheduling come sharply into focus when, as is about to happen to Scotland, they face two pool games in quick succession.

Scotland's plight is particularly acute as their upcoming matches with Russia and Japan -- just four days apart -- will make or break their bid to qualify for the quarter-finals.

Scotland started Pool A with a woeful 27-3 loss to Ireland before a 34-0 bonus-point victory over Samoa in Kobe on Monday revived their last-eight hopes.

Now they need two wins -- and at least one bonus point -- to seal a place in the knockout phase, with everything set to hinge on a likely 'winner takes all' clash against well-rested Japan in Yokohama on October 13, assuming the hosts beat Samoa on Saturday.

But Blair fears the consequences for Scotland of playing two key matches in such a short space of time.

"I think bigger World Cup squads would certainly help. It's a challenging position to be in," he said.

"You leave yourselves a little bit vulnerable in some positions when you cut down to 31 men," the former Scotland scrum-half added.

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

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

Scotland head coach Gregor Townsend and his staff face a tricky balancing act, with Blair admitting: "It's obviously a challenge.

"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."

He added: "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."

Scotland will have to win three games in a row at a single tournament for the first time since 1999 if they are to reach the knockout phase of this World Cup.

But Blair was heartened by the manner of Scotland's win over Samoa following a dire defeat by Ireland.

"We have obviously got a bit of momentum from the Samoa game," he said.

"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."