Felipe Nasr admitted he was "surprised" that Sauber did not opt to alter his strategy, as he trailed team-mate Marcus Ericsson at the Spanish Grand Prix.
Nasr moved ahead of Ericsson at the start but was on a two-stop strategy, while the Swede was placed onto a three-stopper.
Ericsson passed Nasr during the final stint and went on to finish 12th, three places clear of Nasr, who moved up to 14th post-race when Renault's Kevin Magnussen was handed a time penalty.
"It was a difficult weekend," said Nasr, as Sauber's run outside of the points continued.
"I had a good start to the race, and I was able to gain some positions on the first lap.
"I was surprised we did not change from our initial plan - a two stop strategy - to a three stop strategy.
"I do not think the two stop strategy was the right choice, as I could not keep up the pace.
"The stint was too long on the Medium tyres, and I lost all the track positions I gained at the beginning of the race."