Ronan was stretchered off after 13 minutes with a knee injury and, despite tries from Johne Murphy and Wian Du Preez and 11 points from the boot of Ronan O'Gara, the Munster coach has warned his side to be wary of the vengeful Saints.
A last-gasp O'Gara drop goal in the first round of fixtures in November will still be fresh in the English side's minds according to McGahan, who is eager to secure a home tie in the quarter-finals.
He said: "We know that's there and we just need to finish it off. Nobody's harder on the group than the group itself. They know they have things to work on. It wasn't a jubilant dressing-room afterwards.
"We recognise the challenge that awaits in Northampton next week. They're looking for revenge. We need to make sure we step up a few gears."
A club statement on the injury to Ronan added: "[Niall] Ronan had a scan today that showed he's suffered ligament damage to his left knee but he will have to have further examination before the full extent of the injury can be ascertained."
63x46.png){kind=logo}