That defeat brought an end to the Lions’ Challenge Cup campaign, shifting full attention to the URC, where Ivan van Rooyen’s side remain firmly in the play-off race with 21 points.
With little separating teams in the middle of the table, Roux says the focus on matchday is on delivering an 80-minute performance rather than getting caught up in calculations.
"We really had a good week and were focused on the Ospreys. I think it sounds like a cliché, but it truly is taking it one game at a time and not looking too far ahead. We had a thorough review of Perpignan, and obviously the big focus on this week is on this match because it's a crucial game."
The Lions start the day sitting seventh on the URC standings with 21 points from eight matches, while tonight’s hosts, Ospreys, are ninth on 19 points heading into kick-off.
Roux says conditions will be a major factor this evening, adding that adapting quickly to the Welsh weather will be key after the challenges they faced in France last weekend.
In team news, centre Henco van Wyk reaches a major milestone this evening as he earns his 50th cap for the Lions.
Springboks Asenathi Ntlabakanye, Morné van den Berg and Quan Horn all return to the matchday squad for the clash with the Ospreys.
Ruben Schoeman starts in the second row alongside Ruan Delport, with Etienne Oosthuizen named among the replacements.
Roux also confirmed that hooker Franco Marais has flown back to South Africa after suffering a concussion in a freak training accident earlier in the week.
"Franco Marais suffered a concussion in a freak accident during one of our sessions in France, so he has already flown home. Otherwise, we're looking good and actually feel quite healthy at the moment."
Lions prop SJ Kotze says the squad has had to adjust to much colder conditions and adds that forward dominance will be critical tonight, with the set-piece expected to play a decisive role, as is often the case on Northern Hemisphere tours.