The first leg match at Reading ended in a 20-13 victory for London Irish but Gold expects Narbonne to be a much tougher nut to crack at Parc des Sports et de l'Amitie.
"We will certainly find out soon enough if seven points is enough," said Gold.
"We were a bit off the pace in the first leg and we will have to lift our game and put in a much better performance otherwise we will be beaten.
"Narbonne are very strong up front, with a good scrum that provides the platform for them to unleash their dangerous backs. They also targeted the driving maul against us and were pretty successful with that on a few occasions.
"Overall they are a very good team and the two sides are pretty evenly matched so, accepting that French sides are always a lot tougher to crack on their home ground, we are under no illusions about the size of the task we face over there.
"And judging by their reactions at the whistle on Sunday, they seemed happy enough with a seven-point deficit.
"However, we want to win the tournament. It is one of the ways of qualifying for the Heineken Cup and we want to be there again next season. But at the moment we are just focusing on what we have to do in France this weekend."