For a number of weeks, it has been speculated that the pair - particularly Nkunku - would be ready to return to action after prolonged injury layoffs.
Nkunku has been unavailable since the start of August with a knee injury, while Lavia sustained ankle ligament damage during the September international break.
As a result, both players are still waiting to make their competitive debuts for the Blues, with the expectation being that it will come in the near future.
At one point, it was claimed that Nkunku may make the Newcastle United fixture on November 25 or, failing that, the showdown with Brighton & Hove Albion last weekend.
However, the former RB Leipzig star remained absent for both encounters, and Pochettino told reporters at a press conference on Tuesday that there had been no change with regards to his availability.
The Argentine said: "We want to have the player as soon as possible, but I think that we need to be careful. Of course, when he is ready, he will be with the squad.
On Lavia, Pochettino added: "Romeo is doing well, also. but, like with Christophe, he is not going to be involved for tomorrow."
He said: "Lesley feel something last week, it is a minor injury like Noni. That was post-match Sunday against Brighton. It is a minor problem, but we hope that soon they will again be available to train and available for the team."
On the flipside, though, Conor Gallagher must serve a one-game ban of his own after being sent off for two yellow cards against Brighton.
Chelsea head into Wednesday's encounter at Old Trafford trailing seventh-placed United by five points in the standings. body check tags ::