Mercedes had enjoyed a promising start to the pre-season, becoming the first team to complete a race simulation and comfortably setting the fastest time seen in Bahrain courtesy of Nico Rosberg.
Ferrari in contrast has kept a low profile, while Red Bull has endured a torrid opening to its title defence.
But Hamilton dismissed the suggestion Mercedes is therefore ahead of the pack, and believes the fight for season-opening honours will be closely fought.
"I think we have a strong package but I don't feel we are guaranteed [to be] the guys ahead," the 2008 world champion said.
"I'm pretty sure Ferrari is very quick, I'm pretty sure the Red Bull is good. Maybe their engine is not as good as ours.
"But I won't be surprised if at the first race there is a difference of a couple of tenths between the first and second team.
"We have a fighting chance, but we just don't know where we are."
Hamilton also said he is also yet to get comfortable in the W05, but acknowledged the sweeping rule changes distorted how much of an impact that could have.
"So far I haven't found a balance that I like," he explained, "but this year we lost so much downforce, so the car naturally feels worse.
"In perspective against other teams it's good.
"The packaging is I feel the best we have seen in the team, [and] it feels the most put together car I have driven here. Let's hope that results in wins."
AUTOSPORT Live coverage of the final pre-season F1 test will resume at 6am UK time on Saturday morning