Scotland call up three Warriors
Coach Vern Cotter decided to bring the three Glasgow Warriors players in as a precaution, with doubts remaining over the fitness of centre Matt Scott.
Scott is having a scan to assess the extent of an elbow injury he suffered while playing for Edinburgh against Connacht last Friday.
Scott started Scotland's opening defeat by England but subsequently injured a thigh in training and was replaced by Duncan Taylor for the following two games.
Dunbar was named in Cotter's initial squad but also suffered a thigh strain which ruled him out of the opening three games. He has now played two matches for Glasgow.
Scrumhalf Pyrgos made his comeback on Sunday as Glasgow beat Cardiff on his 100th appearance. He had not featured for Warriors this season after aggravating a wrist injury during the World Cup, which required surgery.
Brown has recovered from an ankle injury to force himself back into contention.
Scotland squad:
Forwards: John Barclay (Scarlets), Fraser Brown (Glasgow Warriors), David Denton (Bath), Alasdair Dickinson (Edinburgh Rugby(, Zander Fagerson (Glasgow Warriors), Ross Ford (Edinburgh), Jonny Gray (Glasgow Warriors), Richie Gray (Castres), John Hardie (Edinburgh), Rob Harley (Glasgow Warriors), Moray Low (Exeter Chiefs), Stuart McInally, Willem Nel (Edinburgh), Gordon Reid, Josh Strauss (Glasgow Warriors), Rory Sutherland (Edinburgh), Tim Swinson (Glasgow Warriors), Ben Toolis, Hamish Watson (Edinburgh), Ryan Wilson (Glasgow Warriors).
Backs: Mark Bennett, Alex Dunbar, Grayson Hart (Glasgow Warriors), Sam Hidalgo-Clyne (Edinburgh), Stuart Hogg (Glasgow Warriors), Ruaridh Jackson (Wasps), Peter Horne (Glasgow Warriors), Greig Laidlaw CAPTAIN (Gloucester), Sean Lamont (Glasgow Warriors), Duncan Taylor (Saracens), Henry Pyrgos, Finn Russell (Glasgow Warriors), Matt Scott (Edinburgh), Tommy Seymour (Glasgow Warriors), Tim Visser (Harlequins), Duncan Weir (Glasgow Warriors).
