Sergio Perez said his collision with Sebastien Buemi in the Belgian Grand Prix was caused by the Toro Rosso changing its line in front of him.
The contact between the two cars led to Buemi retiring with rear-end damage, and Perez receiving a drive-through penalty.
Buemi was adamant that Perez was at fault for the collision.
"Perez tried to pass me and simply drove into the back of me, which completed destroyed my rear wing and I had no option but to bring the car back to the pits to retire," said Buemi. "I really can't understand what he was doing, as I was clearly ahead of him: it was as though he forgot to brake."
But Perez reckoned Buemi had put him in an impossible position.
"On lap five I was in seventh when Sebastien Buemi changed his line in front of me under braking, I tried to avoid hitting him but couldn't as I had lost downforce," said the Mexican.
With Perez's team-mate Kamui Kobayashi finishing only 12th after a collision with Lewis Hamilton and some pit strategy issues, team boss Peter Sauber was frustrated with how the weekend had ended.
"For us it was a race of missed opportunities," he said. "After a good qualifying I was very much looking forward to the race, but, except for the weather, everything was against us."