Perpignan are level on points with Worcester Warriors at the top of Pool 2, having shared a win and a loss with their English rivals in the December double headers.
They travel to Bizkaia Gernika RT on January 12, before welcoming Femi-CZ VEA Rovigo to Stade Aimié Giral on January 17, desperate to outscore the Warriors.
Perpignan are marginally in the driving seat as if two teams in the same Pool finish on the same number of match points then group honours will initially be decided by who has earned the most number of match points from the head-to-head matches.
Worcester and Perpignan have earned five points each from those contests and if they still cannot be separated then the club who has scored the most tries in the two matches go top - and Perpignan are ahead 3-1 on that score.
However, Hook's injury is just the latest blow to hit Perpignan, who also lost Guilhem Guirado to injury in the defeat.
Earlier this month Hook's Wales team-mate Luke Charteris was ruled out for the season after rupturing knee ligaments.