"We are still in control of the group, but it is disappointing that we lost, especially at home. In the Heineken Cup you want to end up at No 1 seeds and get the eighth team, especially as you know that's the easiest," Madigan told Dave Kelly of the Irish Independent.
"Unfortunately, we gave that up. But the target is still a home quarter-final and that's attainable. We have to be confident we can win in Castres - they'll be a passionate team down there."
Leinster head coach Mat O'Connor said the turn around in scorelines from the six try, 40-7 demolition job at Franklin's Gardens a week earlier to the 18-9 defeat in Dublin was down to inaccuracy and a lack of execution
"I don't think it was complacent - it was inaccurate. We didn't execute, we didn't look after the ball and we were our own worst enemy," said O'Connor.
"We took our eye off the ball a little bit. We need to make sure we build into Heineken rounds five and six really well."
"It was a pretty tough game of footie. They threw everything at us, they came to be as abrasive as they could, so if you're a little bit inaccurate under those conditions, you get found out.
"They're a good side, they're no mugs. They're a good team and we were second best - that's sport, isn't it? There's three or four opportunities where we could have scored in that final sequence, but we didn't.
"We need to win the next two - if we don't, you're in the lap of the gods. We need to make sure we get results against Castres away and Ospreys at home. And if we do that, we'll win the group and give ourselves the best chance."