The hunt is on to find a replacement for leg-break victim Alex Allan and take up a prized Macphail rugby scholarship in New Zealand.
A training accident has meant Edinburgh prop forward Allan being forced to withdraw a week after being nominated.
The opportunity to travel alongside Glasgow stand-off Finn Russell is likely to go to another forward, possibly within the Edinburgh squad.
That could mean a call to one of several up-and-comings including 21-year-old back-rower Hamish Watson, who has burst on to the scene this season.
Another option in the same position as Allan would be Robin Hislop who has also made strides, including in the European Cup, while Phil Cringle, at 18, is highly regarded and still on a youth development contract,
Capital second row Rob McAlpine is another strong candidate.