Vellacott joined Warriors from the Exeter Chiefs Academy in the summer and has been on loan at National League Two South leaders Hartpury College.
The pair could be up against Warriors Academy star Max Stelling on Friday 7 February, when Scotland take on England at Netherdale.
Scotland Under 20 fixtures:
Friday 31 January: Ireland v Scotland, kick-off 7.05pm
Friday 7 February: Scotland v England, kick-off 7.30pm
Friday 21 February: Italy v Scotland, kick-off TBC
Friday 7 March: Scotland v France, kick-off 7.30pm
Friday 14 March: Wales v Scotland, kick-off 7pm