English clubs' proposal to condense the Six Nations into five consecutive weeks would be "impossible" for players, Scotland full-back Stuart Hogg says.
The two current rest weeks would be scrapped under the reported plans.
Any changes would come in as part of plans for a global season from 2020.
"The injuries that happen in Tests, the physicality of rugby now - for that to be [occurring] on a weekly basis, for me, is pretty much impossible," Hogg told BBC Radio 5 live.
It is believed English clubs presented the proposed changes at a World Rugby meeting in San Francisco in January, at which the governing body discussed the potential shape of a global calendar to come into effect after the 2019 World Cup.
That calendar could see greater alignment between northern and southern hemisphere domestic seasons.
Former England coach Sir Clive Woodward believes a five-week Six Nations would help northern hemisphere teams compete with their southern hemisphere counterparts by replicating the final stages of a World Cup.
Hogg's concerns over player welfare were echoed by team-mate Tommy Seymour.
"If we were playing Wales last weekend we certainly would have been short on numbers, we've already ruled a few guys out of the entire tournament so if you're talking about short-term injuries we definitely would have been short," said Seymour.
And former Scotland scrum-half Rory Lawson said support staff would have similar doubts about players' ability to play Test matches every week.
"I bumped into Stevie Much, an old physio of mine and who's been around the Scotland squad forever, and he suggested that over half of the Scotland squad wouldn't have been able to back it up again," said Lawson
"He said, 'any claims you can condense it into five weeks are madness'."
Scotland face Wales at Murrayfield on Saturday, with kick-off at 14:25 GMT.