Scotland prop Darryl Marfo, one of the finds of their autumn series, is likely to miss at least the first two matches of their Six Nations campaign.
The Edinburgh loose-head, 27, has not played since emerging from obscurity to start all three November Tests.
A specialist deemed earlier this week that an ongoing back problem does not require surgery, but further treatment.
“Hopefully it will start to settle but at this point there is no return date,” said Edinburgh coach Richard Cockerill.
“He is still having treatment and will just continue with his rehab. There is nothing else that needs to be done – no surgical procedure.
“Hopefully he will come back to us as soon as possible.”
Scotland’s – and Edinburgh’s – resources at loose-head are already stretched to breaking point.
Allan Dell, who won 10 caps last season and made a brief appearance for the British and Irish Lions on their New Zealand tour as one of the so-called “geography six”, will be unavailable until the end of February, and therefore miss at least the first three rounds of the Six Nations.
There is also no prospect of the experienced Alasdair Dickinson returning to action any time soon, Cockerill confirmed.
Rory Sutherland, the fourth Scotland loose-head on Edinburgh’s books, has at least shaken off a shoulder problem to start Friday’s European Challenge Cup match against Stade Francais at Murrayfield.
Sutherland, 25, won three caps in 2016 before a groin injury kept him out for 14 months.
He is likely to compete with Glasgow’s Jamie Bhatti and Gordon Reid of London Irish for Scotland’s number one jersey in the Six Nations, with head coach Gregor Townsend announcing his squad on Tuesday.
Townsend’s options are also severely hampered at tight-head prop, with Edinburgh’s WP Nel likely to miss the entire Six Nations with a fractured arm, and Glasgow’s Zander Fagerson out of the first three rounds after injuring a foot when a bench fell on him in training.
Edinburgh’s Simon Berghan, meanwhile, who started Scotland’s last Test against Australia, is banned for the opener against Wales in Cardiff.
With his three front-line options all unavailable, Newcastle’s Jon Welsh is in line to win his first cap since the 2015 World Cup.
Edinburgh’s Murray McCallum, an age-grade international at loose-head who has been pitched into service at tight-head for his club, is another mentioned as a possible contender for a place in Townsend’s squad.
But Cockerill queried whether the 21-year-old, who joined a Scotland training camp last summer, is ready for the demands of the Test arena.
“He played well last week but he is still a young player who has to find some consistency,” said the former England hooker.
“He is a great lad who would certainly give it a good crack, but is he really ready for international rugby? Probably not.
“But as Darryl Marfo showed in the autumn, if he is called upon, he might step up and surprise people.
“It will be a big test for him on Friday against a very good Stade Francais pack, and if he does well there, he might give the selectors something to think about.
“They might want to have a look at him for a training week but I would say it is a bit too soon for him to go down to Cardiff and play tight-head.”