Fernando Alonso completed just three laps in FP1 for the Belgian Grand Prix as power unit problems prevented any further running.
Honda has brought a major power unit update to the race at Spa-Francorchamps, with the Japanese engine manufacturer spending seven development tokens on internal combustion engine, turbo and compressor upgrades.
Both drivers have the new power unit, but Alonso carried out just three laps at the start of FP1 before his running was ended by a water leak. McLaren investigated the issue and ruled Alonso out of the rest of the session as it decided a power unit change is needed.
The two McLaren drivers are already on their fifth power unit components of the season as a result of the Spa upgrade, meaning any new parts that are required could carry a grid penalty.
Button completed fewer than 20 laps in the other McLaren, finishing FP1 down in 18th place some four seconds slower than Nico Rosberg's best time in the Mercedes. Button only used the soft compound, compared to Rosberg's lap being set on the supersofts.
AS IT HAPPENED: Belgian Grand Prix - FP1
Romain Grosjean column: More motivated than ever
Chris Medland's 2016 Belgian Grand Prix preview
How Eric Boullier keeps McLaren on its toes
Keep up to date with all the F1 news via Facebook and Twitter
