Haas Formula 1 team principal Gunther Steiner says the uncertainty in the driver market is making the American squad's decision harder.
Former grand prix drivers like Esteban Gutierrez and Jean-Eric Vergne are believed to be in contention for the seats with the team, which will line up on the grid next season.
Haas has also expressed interest in Force India driver Nico Hulkenberg.
But the with driver market stalled as Ferrari waits on making a decision on Kimi Raikkonen's future, Steiner says it is not easy to get anything finalised.
"We are talking with like 10 people," said Steiner. "Some are higher up the list, some are lower, but we also want to see who is out there.
"It's still difficult to find out who is actually available, because it hasn't been decided who is going where. Everybody's talking, but there's not talking only from our side.
"People are talking back to us: they try to sound out what would be available. It's a little bit of getting in touch with people."
He said the ideal situation for the team would be to have its line-up finalised by next month.
"We would like to make a decision by the end of summer," he added. "Then we can get prepared for the driver. We need to have time to explain to our driver what we are doing, because we are new.
"So by September I hope we have made a decision for at least one, if not two. The ideal would be two.
"We have interesting candidates, which is nice for us, to have drivers with a good reputation talking to us seriously. I hope we can pull some of them off."
Steiner added that he's been pleased by the receptiveness that drivers have shown following an approach by the new team.
He said: "There was a good response when we contacted them. No one was like 'hey, this is new, I don't want to go there'.
"It's like 'hey, tell me what you are doing. It sounds to me like it's a good programme what Mr. Haas has put up here'."
Steiner insisted that an experienced driver was key for the team, suggesting his knowledge would be more important than his speed.
"We need some known quantities. Everything else is new. The whole team is new people put together. It's a lot of unknowns so we need a known quantity in there to tell us 'hey guys, I think the car is good, but this part of the team doesn't work'.
"We need somebody who can actually see where we are at, so we need experience. And if the experience is coming with speed, even better."