The struggling team's best result in Friday practice at Sakhir was Jenson Button's sixth place in the morning.
The Briton slipped outside the top 10 later on, while Perez did not make it above 11th all day.
"I think it's going to be a very difficult weekend for us," said Perez.
"This is pretty much where we are. If we find a couple of tenths, we won't really move any further forward.
"Hopefully we can work something out for the race, because in qualifying we're going to be fighting to get into Q3.
"I think it will be a great performance if we can get into Q3 and score some points. I think that is a realistic target for this weekend."
Button admitted that the Sakhir track brought in the worst in McLaren's difficult 2013 car, though he was optimistic that he had found ways to be more competitive for Saturday and Sunday.
"It's very difficult to get it set up around here," said Button.
"I don't think it's any secret that we are pretty weak in terms of traction and lateral load traction, so this circuit's tough for us.
"We'll make the best of it, but today's been pretty tricky.
"I think we'll get there in the end. We were trying lots of things today, and it's so difficult with the limited running you can do.
"I've got a good feeling already that we've found a set-up that we'll be running tomorrow that will be more competitive."
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- Jenson Button