The four-times world champion will start ninth in his Mercedes due to a five place grid penalty for an unscheduled gearbox change after setting the fourth-fastest time in Saturday's qualifying.
His Ferrari rival Sebastian Vettel, meanwhile, who won in Melbourne two weeks ago to take the early championship lead, will line up on pole.
"I have no idea what's going to happen in the race," Hamilton told reporters on Saturday.
"I just hope that we're moving forwards. Hopefully, I'll be able to get up at least to where (Daniel) Ricciardo is and then overtaking from then on is going to be very tough."
The Bahrain race has never been won from lower than fourth. Hamilton's Mercedes, too, is no longer as dominant as it was early in the turbo-hybrid era.
Overtaking, with Formula One's wider cars and increased downforce introduced last year, has also become more difficult as the race in Melbourne demonstrated.
The 5.4-kilometer long Sakhir circuit with its long straights should offer more opportunities but passing will get harder the higher up the order.
"I haven't really thought about it yet," said Hamilton.
"I'll get to it and if I can overtake, I'll overtake. If I can't, I can't. What will be, tomorrow, will be."
The 33-year-old is set to start Sunday's race on more durable soft tyres even as his rivals start on the super-soft.
That should theoretically allow him to go longer in the race before needing to pit, opening up strategic possibilities Mercedes might be able to exploit in the event of a safety car, like Ferrari did in Australia.
The Italian team, who also have Kimi Raikkonen second on the starting grid, appear to be the ones to beat in Bahrain and Hamilton's hopes could well be pinned on just such an upset.
"The race is the race and everything can change as we know and this makes the sport so exciting," said Mercedes team boss Toto Wolff.
"From pure pace tomorrow, I would say the two Ferraris are clearly the favourites."
(Editing by Christian Radnedge)
