Centre Matt Smith says Leicester Tigers will lose to Northampton in the play-offs unless they improve dramatically on the 32-23 win over London Irish.
An eror-strewn display saw Tigers trail 23-12 with 10 minutes left.
But they rallied to secure top spot in the regular Premiership season and set up a play-off semi-final game against Saints at Welford Road on Saturday.
"We know if we play like that again, we will be on holiday on the Monday," Smith told BBC Radio Leicester.
"We have a lot to look at during the week and hopefully we can put in a lot better performance next week.
Tigers gifted Irish winger Topsy Ojo two intercept tries and missed countless chances of their own as the Exiles led at the interval.
But three tries in the closing stages ensured a stunning victory.
"There were a lot of unforced errors - there are no excuses but we looked a little bit rusty," Smith said.
"I think we were a bit guilty of playing a bit too much - especially in the first half. If you get turned over in your own half there will always be chances for the opposition.
"We never seem to make it easy for ourselves. There are a lot of lessons to learn."
Director of rugby Richard Cockerill was furious with his side's sloppy showing.
"He gave us all a bit of a telling off," Smith added. "He told us we weren't good enough, we were lucky to get the win and if we play like that again we will be knocked out."