Heenan injured his shoulder in his first GUINNESS PRO12 match of the season against the Newport Gwent Dragons and faces five months on the sidelines.
The New Zealander joins Sean Henry in the treatment room - the hooker looks to have ruptured ligaments in his knee, while Danie Poolman is not at full fitness with a head injury.
But Lam says the situation is nothing new for Connacht, having suffered a similar injury crisis last season.
"At this stage at openside we have Willie Faloon and the academy [players]," he told the Irish Times.
"If I was Toulon, yeah, I would be buying someone, but we are not. Everyone wants to have strength in depth.
"It affected us last year with Willie not being there for a long period. Jake had a big workload. It's such a crucial position."
Lam's side host Leinster on Friday evening looking to make it three wins from three.
And the former Samoa international admits the gulf in experience between the two squads will provide Connacht a real challenge.
"Look at their side," he continued. "That is the challenge; we have only two guys who have started internationals (John Muldoon and Robbie Henshaw). We know we are up against it, but we certainly won't lie down.
"There is no doubt you put their squad up against ours, they should win every time, but if we perform well, we give ourselves a chance.
"Some guys have the advantage when they have played 50 tests - it's easy - like riding a bike."
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