MONTMELO, Spain (AP) Formula One champion Lewis Hamilton had to cut short preseason testing on Thursday after feeling ''unwell,'' according to Mercedes.
''An unplanned stoppage keeping us off track at the moment. Lewis Hamilton is unwell and not able to continue driving today,'' Mercedes said on its Twitter account.
The Barcelona-Catalunya Circuit press office said Hamilton had to stop driving because of a fever.
Hamilton had completed 11 laps on the first day of the second preseason tests.
Mercedes reserve driver Pascal Wehrlein took over for the rest of the session. Mercedes had allowed Wehrlein to drive for Force India, meaning the German drove for two different teams on the same day.
''We've borrowed him back from our friends Force India F1. Thanks guys!'' Mercedes said.
Hamilton is scheduled to return to driving on Saturday.