Underwood twisted his left knee during the 20-13 victory at Bath last Saturday and was carried off in agony. He will undergo a hospital scan on the injury, but early indications are that he could be out for two weeks.
Stuart Legg, who scored the winning try against Bath after replacing Underwood, is expected to keep his place in the Newcastle side when Northampton visit Kingston Park.
England's reserve hooker, Phil Greening, has been given a vote of confidence by Gloucester after his half-time substitution against Bristol last weekend. Greening, who was replaced in the second half by the new recruit Neil McCarthy, will play against Leicester at Welford Road on Saturday.
The director of coaching, Richard Hill, has named the same team - including replacements - which started the 35-13 win against Bristol.
The Scotland stand-off Duncan Hodge will make his first appearance in an Edinburgh jersey this season when they play the Welsh side Llandovery on Friday. Hodge has been refreshed by the extra break after returning from Scotland's summer tour of South Africa and is now ready to return.
The Edinburgh coach, Bob Easson, also gives first run-outs to the Scotland caps Cammie Glasgow and Stuart Reid, and the Boroughmuir prop Ross McNulty, a member of the Silver Thistles party in New Zealand this summer. Edinburgh also go into the match with a new captain in the scrum-half Graeme Beveridge as they complete preparations for their first European Conference match in Perpignan a week on Saturday.Reuse content