Former Falcons Craig Hamilton and Phil Godman are on the bench and Borders pair Bruce Douglas and Kelly Brown are at prop and flanker.
Grimes's withdrawal means there are only seven Newcastle Falcons players in action this weekend.
England centre Jamie Noon has been named in the Martin Johnson XV for the Nobok Challenge against a Jonah Lomu XV at Twickenham tomorrow.
Gregor Townsend, who has returned to the Borders from Montpellier will be at full back and Falcons Player of the Season Matt Burke in the centre for Lomu's side.
Falcons back rower Colin Charvis starts at openside flanker for Wales against the USA at Rentschler Stadium, Hartford, tomorrow and Charvis has been named vice captain for the match.
Newcastle's American second row Luke Gross packs down for Rob Howley's Rest of the World XV at Cardiff's Millennium Stadium on Sunday against Scott Quinnell's Britain and Ireland XV. Former Falcons wing Epi Taione is also on the bench for the Rest of the World squad.
Falcons sevens specialists Mathew Tait and Phil Dowson will also be in action in the IRB Emirates Airline London Sevens at Twickenham this weekend and academy wing Cameron Johnston makes his full Scotland Sevens debut.
Academy player Johnston makes his international Sevens bow in the event.
Meanwhile, the Falcons will play in Tokyo's National Stadium on their Japanese tour in August. Newcastle's GTF Cup match against current Japanese champions NEC is on Saturday, August 20, at the National Stadium, kicking off at 7pm local time (11 a.m. UK time) and will be part of the Greater Tokyo Festival. Then on Tuesday, August 23 the Falcons move to Nagoyas Toyota Stadium to take on Toyota in the Expo Cup, kicking off at 7.30pm.
The Falcons will also hold a coaching clinic for local children on Thursday, August 18 at Tokyo's Chichibunomiya stadium, where the Japanese national rugby side plays many home Tests.
The name Chichibunomiya commemorates Prince Chichibu, who was not a rugby player but was passionately fond of the game.
The Falcons complete their preparation for the new Guinness Premiership season with a friendly against Glasgow at Kingston Park on Saturday, August 27, (kick-off 5.30pm).
Tynedale and Falcons prop Jonny Williams, former Tynedale flanker James Ponton (Sedgley Park) and Northumberland County captain Ed Thorpe (Otley) plus Alnwick's Danny Hodgson, assistant manager, all fly out with the England Counties squad today on a tour to South America.
They take on an Argentina XV and provincial side Rosario before facing the Uruguay national side in Montevideo.
A North Tyne Barbarians side takes on Northern Pirates tomorrow at Border Park (2.0) to raise money for the Ali Johnson Trust. For details on taking part or supporting it, please contact Steve Turnbull on (07970) 570-010.
