Zhou Guanyu qualified an impressive fifth for Alfa Romeo at the Hungaroring, split from his team-mate Valtteri Bottas by Leclerc in the Ferrari.
The Monegasque driver's team-mate Carlos Sainz didn't even make it to Q3, ending the Q2 session in 11th place after missing out by just 0.002s.
Asked if he was concerned about the team's pace given he felt he had put on a good lap, he said: "It's not really a concern in the way I feel like it's very difficult to expect the pace of others from qualifying to race, from track to track.
"We've got surprises every weekend, I did not expect to have an Alfa Romeo in front of me for the race tomorrow, so I don't know how they will be in the race."
Regarding Alfa's surge in form, he added: "They were very strong, yesterday the team showed me the simulations of what we think they will be like, and honestly they were alright, the simulation ahead of today.
"And yesterday I was like, 'there might be something wrong in that and it might be a mistake,' and they proved me wrong today because the team expected it.
"Again, we have a lot of work to do. It's very difficult to understand because of my knowledge, I haven't checked, but I don't think they had any particularly big upgrades for this weekend.
"But then from one weekend to the other, everybody is changing and struggling one weekend and fast the other, so it's very difficult to understand."
Sainz stressed that his struggles in Q2 were due to a "weird" feeling on the medium tyre.
"I've been feeling a bit weird with that medium compound all weekend," said the Spaniard.
"Every time I was running it, for some reason we were always struggling a lot in sector one, getting them to work. It was even harder than the hard tyre.
"So I knew Q2 was going to be a tougher session for us. Q1 we got through nicely, but then as soon as I put that compound again in Q2, I was just sliding a lot in sector one, and never being able to put a decent lap together.
"I mean, the lap wasn't too bad, but I just lacked quite a bit of grip. A shame, but it was only two-thousandths, which in this new F1, those two-thousandths cost you a lot."
Regarding the pace of some of his rivals Sainz said: "McLaren, Alfa Romeo, they are all quick here this weekend.
"I don't know if it's a track special or is just simply a matter of track characteristics, us not nailing the car set-up or the tyre preparation, we need to analyse.
"But we've been on the limit all weekend with the medium compound and even in all compounds, we've just haven't been top four, top five, how we should or how we used to be."
