The seven-time world champion endured a difficult opening day of practice at Barcelona, as Mercedes had its first proper run on a regular circuit of new upgrades following their introduction in Monaco.
Hamilton ended second practice 11th fastest overall, 0.642 seconds adrift of pace setter Max Verstappen, with team-mate George Russell less than two-tenths quicker in eighth.
But with the fight behind Red Bull looking extremely close, Hamilton says that a lot of work is needed ahead of Saturday if he is going to get safely in to Q3.
“I think from the pace that I have today, it's a struggle for me currently to get into top ten,” he explained. “But hopefully, we'll do some changes overnight.
“I think it's very, very close between us in that P5 back to P10 [position]. It's impressive to see the improvements that everyone seems to have made all around us.
“If we look at [Esteban] Ocon, the Alpines are doing great. We saw the Aston Martin is second right behind the Red Bull, which is really, really impressive. So it's not going to be easy, that's for sure.”
Team-mate Russell was slightly more optimistic about the situation Mercedes found itself in, as he pointed out that the squad often faced difficult Fridays before its pace ramped up over the remainder of the weekend.
“We know that we're not Friday specialists,” he said. “We often take a bit of a step forward on Saturday and Sunday, and it's the right way round for it to be.
“But we are where we are. I think a lot of people are bringing updates to the car and we weren't expecting to suddenly set the world on fire.
“We just need to learn what we can from the info we've got and try and move forward tomorrow.”
Russell conceded, however, that there were other cars – especially the Alpine – that looked very competitive on low fuel.
“I think the Alpines are looking really strong,” he said. “So, between us, Ferrari and Alpine, it's probably going to be tight. Then maybe you've got Nico [Hulkenberg], who was really quick today. I don't know where that came from.
“But we saw that in Miami, I think, Kevin [Magnussen] qualified ahead of us but then things changed on Sunday.
“I don't expect us to be having an incredible day tomorrow. But I certainly expect us to be having a better Sunday than Saturday. So yeah, that's what we're gearing up for.”
Hamilton agreed that early indications from running on Friday pointed to Mercedes struggling more with its single lap pace than long-run form.
“I think the long run pace didn't look terrible,” he said. “We have just got to work on trying to figure out how we can extract more on a single lap.”
