Sauber has recalled Adrian Sutil to drive tomorrow morning after a disastrous third day of the final pre-season test in Bahrain.
Sutil suffered an engine problem on his installation lap in the morning and the decision was made to change it, meaning that the German failed to complete a lap today.
The team had planned to give team-mate Esteban Gutierrez the full day, but because of the engine problem the decision has been made to split Sunday between the two.
"Unfortunately today we have encountered an anomaly on the engine and as a precautionary measure we decided to change it, which meant we could only manage one lap in the morning," said head of track engineering Giampaolo Dall'Ara.
"However, assembly takes considerably longer and at a certain stage during the afternoon we decided to focus on tomorrow and be ready for the final day of testing."
Gutierrez, who drove yesterday, was upbeat about the progress the team was making, but still felt Sauber had a lot of work to do.
"Overall, we've been making some progress," said Gutierrez.
"Today, we didn't look at performance, we looked more at racing and going through procedures, covering areas to prepare for the race for the mechanics and engineers.
"We managed to complete our full programme, which is a positive, but obviously we still have a lot of work to do in terms of the car, the reliability.
"There is nothing specific, we just need to keep doing the steps we are."