Yasuhisa Arai says Honda needs to put "ourselves in the right place first" before supplying a second team with engines.
With Renault ending their engine deals with Red Bull Racing and Toro Rosso at the end of this season, both outfits are in the hunt for a new supplier.
The duo are leaning towards Ferarri however there are some rumours that Toro Rosso try for Honda power.
Honda, though, have all but ruled out that, conceding they need to up their game before they can supply a second team.
"It is difficult for [Toro Rosso] to come to us," Honda motorsport boss Arai told F1i.com.
"It is difficult, looking at the maturity of the power unit it is very difficult. We have to put ourselves in the right place first."