Eoin McKeon, who suffered an ankle sprain last week, is among the new injury concerns and likely to be out of action for up to two weeks.
The young back rower is joined on the sidelines by out-half Miah Nikora who is also unavailable this week due to a shoulder injury.
Lam, who will announce his team on Friday, said: "I know Zebre are going to be desperate for a win. We know that, it has been a long time for them, so we know what's coming.
"What Eric (Elwood) did last year in getting to eighth (in the league) was massive. But we can't focus on that. We want to get better. It's about the performance we put on every weekend."
Zebre will be buoyed by the fact that the last two times the teams met there was less than seven points separating them. The Italian outfit have recruited well in the summer and should pose a much stiffer threat this season.
Tickets for the Connacht v Zebre encounter are on sale now from the Connacht Rugby offices, online at tickets.ie and in Centre and SuperValu stores province-wide.