Jean-Eric Vergne said he was forced to pit for new tyres near the end of the Monaco Grand Prix because the Pirellis he was using were simply too worn out, rather than because Toro Rosso was gambling on rain.
The Frenchman was running strongly in seventh position in his first Formula 1 race in Monaco when he pitted for intermediate tyres with just six laps to go.
The move did not pay off, however, as there was insufficient rain to make his tyres work, and the Toro Rosso driver dropped down to 12th position.
"I ran at a very good pace, which I am happy about and I was as high as seventh," said Vergne. "I was lapping quickly and consistently. But with around 14 laps to the end, my tyres were completely gone and I had to come in for the intermediates, but the rain was not strong enough.
"It's a real shame about the laps I lost in traffic at the start because without that I could have been comfortably in the points today.
"I am looking forward to Canada, as it's a track I particularly like even if I have not been there and I will go there really hungry to get a good result."
Team boss Franz Tost said the squad had no choice but to make Vergne stop for new tyres when he did.
"As he had very little grip on the worn tyres, we brought him to fit the intermediates on lap 71, but the rain which would have helped him fight for tenth place did not come soon enough," he said.