The Tigers visit Ashton Gate on Easter Sunday (15:00 BST) in what is set to be key clash in the race for the Premiership top four, with third-placed Leicester five points behind the Bears.
Bristol have not played since the 53-28 defeat by neighbours Gloucester three weeks ago, in which the Cherry and Whites scored four unopposed tries during the first 17 minutes, and ended the match with nine.
Lam also pointed to his side’s victory over Exeter the week before as evidence of where they need to tighten up their defence after also conceding six tries.
“It was a really good wake-up call for us,” said Lam. “The Exeter game as well, our defence was exposed even though we played well, we conceded 24 points in 17 minutes.
“I do believe it’s an anomaly the way we played that [Gloucester] game and I think after a few days off, coming back, what I did love about it was there was a lot of hurt in the team and I saw the bounce-back in training.
“I’m confident that we certainly won’t be that bad again this year.”
