Honda does not have any potential customers for its new F1 engine, boss Yasuhisa Arai has admitted.

After a six-year absence, the Japanese carmaker's plan had always been to return to the sport this year and only supply new works partner McLaren.

But for 2016, Honda is open to adding paying customers to the roster.

"If (other) teams want to use our engine or power unit," Arai said a year ago, "we can deliver (that) after 2016."

Fast-forward to late February 2015, however, and Honda is embroiled in a tumultuous preparation for the new season, beset by constant technical problems.

Arai admitted to F1i.com that testing has been "like a pop-up game", as when one problem is solved "another one pops up".

The idea of adding customer teams to the books for 2016 is therefore on the back-burner for now.

"We don't have any offers from any team to be a second team," Arai confirmed.

"Maybe it's because they think there's something a bit mysterious about Honda."

What he means is that, beneath the teething troubles, Honda's actual performance remains basically unknown, but last week at Barcelona some signs of progress could be seen.

Arai admits Honda is indeed starting to show potential customers "a little bit of our good capability and good feeling".

"But it's a very difficult question," he added, "because I am wondering can we prepare for supplying a second team during the season? I don't know."