Brive play their final qualifier at home to Overmach Parma on Thursday, almost 48 hours before Ruddock's men take on the Italians.
However, the Director of Rugby insists his team must first focus on the game and respect a talented Petrarca side before they look to overtake Brive.
"The difficulty with a situation like this is if you go out thinking about getting bonus points and racking up tries," he said.
"There is the risk that you don't respect your opponents enough and it ends up being a banana skin for you.
"Petrarca beat Bourgoin home and away, which is something we didn't manage to do, so you have to respect them as serious opposition.
"They have got a lot of Premiership experience in their ranks with people like Nicky Little who has played international rugby and World Cups and also Ludovic Mercier. They are players that can hurt us if we don't watch them.
"So we will focus on improving our game from how we played against Bucuresti Oaks last weekend.
"We got six tries but we could have performed better and we'll be looking to improve our cohesion and build the game on Saturday instead of getting carried away with the permutations."
Ruddock has indicated he will make some changes this weekend as he looks to give his entire squad game time.
He said: "What we will do is rotate the team in advance of the Sale game. Those who were on the bench last week will now start.
"Chris Fortey will probably be on the bench and Aleki Lutui will start. Matt Powell will go in with Ryan Powell on the bench.
"Loki Crichton is also back available for the weekend and will be in the 22, although probably on the bench.
"Joe Carlisle will probably start and it is a great opportunity for him to put a marker down before the Sale game.
"If I can give everyone game time before the Sale game that will be advantageous to us."