This is the second successive campaign Bristol – who reached the play-off semi-finals in June – have lost key players to major injuries.
MacGinty and Ibitoye both also missed chunks of the season last winter.
Bristol reduced the size of their senior squad over the summer to 31 players but Lam said improving their strength in depth to deal with injuries better was key.
Yet he accepted the absences have hit their chances of reaching the play-offs again this season.
“The odds on us getting through to the top four 100% have gone up – that’s why it will be a massive highlight for us this year if we can bounce back from that, which we look forward to doing,” Lam said.
Max Lahiff, James Williams, Noah Heward and full-back Rich Lane are among those also still on the sidelines and the recruitment team are looking at bringing in reinforcements if needed.
“We went into last week’s game not expecting we’d lose those three,” Lam said.
“You’ve got to go in prepared, ‘what if another one goes down?’. That’s what the recruitment team are doing, looking at what’s available, working through the options then pull the trigger if we need to.”
Bristol travel to Saracens on Saturday and Lam stressed they have to quickly move on to the next players coming into the squad.
“You acknowledge this is not ideal but then you don’t dwell on it any more,” Lam said.
“Today is about giving people the context of what we’ve lost but now we’ve already started the process of bringing the next guys in.”
