Northampton director of rugby Jim Mallinder admitted there was plenty of room for improvement after his side opened their Heineken Cup campaign with a nervy 18-14 win over Castres at Franklin's Gardens.
Tries from Bruce Reihana and Ben Foden, added to five points from Shane Geraghty and a penalty from Stephen Myler proved enough but there were far too many errors for Mallinder's liking.
"It was a tough game, Castres played very well and were very physical and we didn't play well," the Saints boss said.
Asked about the reasons for the poor performance, Mallinder said: "You want to get on the front foot but our lineout didn't function.
"We were unfortunate to lose lock Christian Day very late in the day through food poisoning and this affected our lineout calls."
Northampton's goal-kicking in the first half was abysmal with four misses from Reihana and one attempt from Geraghty which barely got off the ground and which may have proved crucial on another day.
Mallinder said: "The goal-kicking was frustrating, both had off-days but last week Bruce kicked four from five and the week before that Shane kicked four from five."
Mallinder complimented Courtney Lawes for his efforts in the first half as the big lock caused problems to the French defence.
"Courtney was excellent in getting us over the gain line but we tried to force the play too much and we need to keep hold of the ball more," Mallinder said. "Allowing Castres a bonus point was not ideal but I'm confident we are still a good side and can go to Edinburgh next week and get a result.
"We won ugly but I'm confident we will do well in this competition and qualify for the next round."