"You would imagine that we will need Castres to have a good performance against Leinster and turn them over and give us a chance the following week. But all we can focus on is what we are doing at Ospreys," said double Heineken Cup winner West.
"We need to concentrate on winning that match. It's going to be a tough game and we know the Ospreys have a squad full of quality. They are in the top three in the Pro 12, as are Leinster, and Castres are in the top three in France, so it's a real tough group.
"It's strange that we are battling away on not too many points but we are playing OK in the group. You hear other coaches talking about going away and getting five points, but it's something that has not come into our heads at all.
"In this group we know every game is going to be hard fought and getting a win is really difficult, let alone a bonus point.
"It was really disappointing when we played that game at home against Leinster. We didn't give a good account of ourselves in the first 15-20 minutes and the game was gone.
"We had lost the game in no time. We played in Castres and felt we did enough there to deserve the win, but we didn't quite get it.
"To go away to Leinster on the back of that loss and turn them over on their own pitch showed that we are a good side and when we get our game right we can compete with anybody. We had quite a few injuries and a suspension and it was tough, but we worked hard, we fought hard and showed a lot of character under pressure and came away with a victory."