With veteran skipper Julien Bonnaire ruled out with a fractured arm at the beginning of the week and a host of other injury concerns continuing to linger, the news that Parra is fit to feature in London is a massive plus for coach Vern Cotter and co.
The 25-year-old France international has been absent with a knee injury since late November and was expected to be out of action for between 10-12 weeks. Parra did not require surgery to correct the damage to his posterior cruciate ligament but Clermont initially reported that he wouldn't return until mid-February.
The former Bourgoin player has beaten that estimated comeback date by a month, though, after Cotter claimed he would begin the crucial clash with Quins in two days' time.
"Morgan will start the game behind the scrum," said Cotter, who was facing a scrum-half crisis after injury to Thierry Lacrampe at the weekend left Ludovic Radoslavjevic as the only fit No9 prior to Parra's recovery.
"He is at 100% and he has been aiming towards this game for a while now. He has the ability to boost his team mates and he will bring a great deal of experience and his usual application to the team."
Ex-All Black wing cum full back Guildford provides another boost after he signed a two two-year deal with an option for a third having been mooted as a possible signing for much of the past few weeks.
The 24-year-old, who has won 10 caps for New Zealand but hasn't featured for his country since mid-2012 following a series of alcohol-related off-field issues, will join from Canterbury at the close of the 2014 Super Rugby season in August.
"This is a tremendous opportunity for us to enrich our team with a player of such talent and versatility," said Clermont backs coach Franck Azema.
"Like all the All Blacks we have in our ranks, we believe that he will bring us a bit of his culture and his feel for the movement of the game, which we want to continue to develop.
"Everyone knows his ability, technique and speed and the explosiveness that he can bring to the attacking line and we're really happy to offer him a new challenge and a first experience in France."
Guildford is Clermont's fifth signing ahead of next season, with British & Irish Lions centre Jonathan Davies having already put pen to paper alongside lock cum back row Sebastien Vahaamahina, hooker John Ulugia and No8 Fritz Lee.