Striker Benteke is still thought to be weeks away from fitness following a recent hip injury suffered against Norwich.
However, Belgium boss Marc Wilmots has selected the big striker for his side's World Cup qualifiers against Croatia on October 11 and Wales on October 15 as his side seek the point they need to secure their spot next summer.
Wilmots has reportedly stated Benteke will not be risked for the Croatia match but, should they lose that and need a result against the Welsh, Benteke is likely to be called upon.
Lambert knows his hands are tied because he could be denied Benteke's services for Villa's first game after the international break should he stop the striker joining up.
"It is up to Marc what he does," said the Scot. "My stance has not changed since last week - he's not playing for us (at the moment). But I trust Christian to make the right decision for himself as a footballer and a human being.
"He's a great kid. I know he wants to get back training as quick as he can.
"Christian has to go. He is obliged to go by the ruling. I have spoken to Christian, we are obliged to let him go. If you don't let them go and they end up playing for us on Saturday and missing the Belgium game then they can end up invoking the rule on us and prevent him from playing for us.
"I think the rule is a mockery. It fits some things and not others. It comes back and bites you.
"You (as the club) are at a disadvantage to a certain extent, you're hoping common sense prevails."
Lambert added: "I totally understand Belgium's prerogative, they're a point away from the biggest tournament at national team level.
"But you're hoping they understand our point of view, the guy's got injured for us and might play for us.
"Marc's been fine - I played against him, I know him from German football. I spoke to him when I signed Christian.
"Christian's probably stuck in the middle, but I've had a good conversation with him and he'll know himself what's right for him.
"There's no worries on that front. I trust Christian to do it.
"I won't be happy if he plays and comes back to me injured after doing ever so well. I won't be happy."
The Scot seemed to question whether it was really worth risking Benteke.
"Belgium have great players, Romelu Lukaku is playing ever so well for Everton so it's not as if (they don't have other options).
"They have two games to get a point and you'd be expecting them to get one from one of them."
Regarding Benteke's fitness, Lambert said: "He's doing really well at the moment.
"He hasn't been out on the training pitch yet. But when he starts to kick a ball, that'll be a test, he'll know himself."