Northampton Saints player ratings: Phil Dowson's side booked a Champions Cup semi-final with Leinster after seeing off an ill-disciplined and quarrelsome Castres at Franklin's Gardens on an impressive 51-16 scoreline.
George Furbank is set to play his first game since fracturing an arm against the Bulls in mid-December.
Northampton Saints have confirmed that Temo Mayanavanua, Juarno Augustus and Fin Smith will return to the starting line-up for Friday’s Investec Champions Cup Round-of-16 fixture against ASM Clermont Auvergne.
England captain Maro Itoje will return to captain a Saracens side containing four of his international team-mates during the Guinness Six Nations when they host Harlequins in the Gallagher Premiership on Saturday.
England fly-half Fin Smith has returned to Northampton Saints' starting line-up a week after the Guinness Six Nations campaign came to a close as his side host Leicester Tigers on Friday in the East Midlands Derby in the Gallagher Premiership.
Saints defeated the north Londoners three times last season and were led out by Nick Tompkins on his 200th appearance for the club, who were dealt a pre-match blow when Elliot Daly withdrew with a hamstring problem.
Thornbury and Spencer were both short-term signings, with Spencer already snapped up by Ospreys ahead of their round two EPCR Challenge Cup game this weekend.
Last season's Investec Champions Cup semi-finalists Northampton Saints got their new campaign off to a perfect start with a 38-8 bonus-point win over Castres at Franklin's Gardens.