Nico Rosberg quickest, Lewis Hamilton investigated

Nico Rosberg edged out Mercedes team-mate Lewis Hamilton to go fastest in Saturday's practice session ahead of the German Grand Prix, with the Brit facing a potential 10-place grid penalty.

Rosberg dominated Friday's two sessions and set himself up for a run at championship leader Hamilton, who overtook him at the top of the drivers' standings following his win in Hungary, with another strong showing.

However, it was Hamilton who set the early pace, going quicker than Rosberg for the first time this weekend with a time of one minute and 16.015 seconds.

Mercedes, however, are under investigation from the race stewards for an unsafe release of the Brit that caused Haas' Romain Grosjean to stop in the pit lane.

There were no such concerns for Rosberg, though, and, on a fresh set of supersoft tyres following a lock-up going into the hairpin, he went 0.057secs clear of Hamilton's new time and could not be caught.

Red Bull and Ferrari remained well-matched, but it was Daniel Ricciardo of the former who came out on top in their battle.

The Australian was within one tenth of leader Rosberg, but team-mate Max Verstappen came in behind Kimi Raikkonen and Sebastian Vettel.

Grosjean suffered a water leak on Friday and his troubles continued on Saturday as Haas were forced to replace his gearbox, while Jenson Button was back in the car for McLaren following an eye problem on Friday.