Rees-Zammit has not played rugby since a European Challenge Cup match on 13 January 2024, before leaving the sport to pursue a career in American football.
He has been training with the Bristol squad for the past four weeks, including on a team trip to Portugal, after signing a one-year contract.
Yet Lam said getting him back to match fitness remains the biggest challenge before the Prem Rugby opener at home to Leicester on 28 September.
“Some of his highlights reels, we’ve seen evidence of that in the training. We’ve got a lot of quick boys but that’s next level quick what he can do,” Lam said of Rees-Zammit’s first weeks in the squad.
“But I think the biggest challenge for him at the moment is just getting back to rugby fitness, he hasn’t trained this way for 18 months.
“He’ll be the first to admit the first couple of days, the first week, he was seriously blown but he’s getting better and better.
“By the time we’ve had that first Premiership game we hope that he’s fully ready to go.”
