Pascal Wehrlein will test for Mercedes on Wednesday in Barcelona after receiving a last-minute call-up to replace Esteban Ocon, who had originally been scheduled to drive.
Mercedes said the reason for the swap was because they requie a driver with "race experience" to evaluate new parts.
It also comes after Ocon drove for Renault on Tuesday, testing the team's new engine, which could help power customer team Red Bull to more victories in 2016, following their first win of the season at the weekend.
Ocon had said he was looking forward to driving a championship-winning car, but it's likely that will now have to wait until the second in-season test in July, after the British Grand Prix.
Full driver line-up:
| Team | Tuesday | Wednesday |
| Mercedes | Nico Rosberg | Pascal Wehrlein |
| Ferrari | Sebastian Vettel | Antonio Fuoco |
| Red Bull | Daniel Ricciardo | Max Verstappen |
| Williams | Alex Lynn | Felipe Massa |
| Renault | Esteban Ocon | Kevin Magnussen |
| Toro Rosso | Pierre Gasly | Daniil Kvyat |
| Force India | Alfonso Celis | Alfonso Celis |
| McLaren | Jenson Button | Stefan Vandoorne |
| Manor | Pascal Wehrlein | Jordan King |
| Haas | Romain Grosjean | Esteban Gutierrez |
