Eddie Jones has claimed Scotland "possibly got their physical conditioning wrong" during their ill-fated World Cup campaign.
Speaking to the BBC, the England head coach suggested that a 32-3 warm-up loss to France hinted at problems Gregor Townsend's team would face during the tournament.
Jones said: "We have great respect for the Scottish team and they way they play. Where they came unstuck at the World Cup is possibly they got their physical conditioning wrong."
Townsend had claimed ahead of the tournament that Scotland would be the "fittest at the World Cup", but Jones felt otherwise.
"The [game against France] gives you a pretty good indication of where a team is going to be. They looked like they had over-ran, but that's a judgement from a long way away," the 59-year-old added.
Where next for Scotland?Jones believes Scotland need to take inspiration from Japan - who recorded their first victory over the Scots with a 28-21 win in their crunch Pool A match - to try and become the "best small team in the world".
Jones, who coached the Brave Blossoms between 2012 and 2015, praised the work being done by Townsend but offered suggestions on where they could improve,
"Gregor's got them back playing how a Scotland side should play. [A lack of size] makes it difficult but you can have one-off success like Japan have had.
"You've got to pool all your resources into being the best small team in the world."
Highlighting the set-piece as an area of improvement, Jones continued: "You [must] look at everything you do, at how you can win ball quickly - particularly from set-piece.
"You look at how you can win the ball quickly from the breakdown and you need a consistent programme for four years to be at your best to do that.
"You have to play quick, you have to have a varied attack and it takes a lot of cohesion to play that way."
Japan in the Six Nations?Jones also admitted Japan's performance in the World Cup - where they advanced to the quarter-finals before being overcome by eventual winners South Africa - had helped them stake a claim for greater involvement in the northern hemisphere's programme of games.
In the aftermath of the World Cup the Daily Mail claimed that plans had been privately mooted to invite Japan, currently ranked eighth in the world, to the Six Nations after The Rugby Championship - the southern hemisphere's equivalent tournament involving Argentina, Australia, New Zealand and South Africa - had proposed a delay of up to five years before sanctioning the Brave Blossoms' involvement.
"I think ten internationals a year [in the northern hemisphere] is about right," Jones said, before warning: "Increasing the Six Nations would mean taking away from somewhere else.
"I'd bring Japan in for bye-weeks, so they'd play two games over the next three or four years to prove they're strong enough to compete consistently."
The Six Nations, originally a British-based tournament featuring the four home nations, was widened to include France in 1910 and Italy in 2000.
More recently, there has been talk of extending the competition once more to include Georgia or Russia - possibly at Italy's expense - but no formal proposals have been put forward.