Mercedes revealed the reason behind Nico Rosberg's slow pit stop during Sunday's German Grand Prix was due to a stopwatch malfunction.

Rosberg was forced to take five-second penalty before his pit stop after the stewards ruled he drove Red Bull's Max Verstappen off the track. 

The German's misery was compounded when a stopwatch failure meant he was stationary for almost double the time he was penalised for. 

Rosberg eventually finished in fourth behind Red Bull pair Verstappen and Daniel Ricciardo, as Mercedes team-mate Lewis Hamilton claimed the win at the Hockenheimring. 

"Even in a Formula One team with all the high-tech, if you get to take out the instruments that you usually don't use like a stopwatch, they can fail," explained Mercedes boss Toto Wolff.

"The stopwatch didn't start properly and once we realised we had to take it safe and this is why it took longer than normal."

“The time thing failed. It didn't function like it should have," he continued. "We could have also counted, one thousand and one, one thousand and two, one thousand and three but we relied on the stopwatch and it let us down."

However, Rosberg said the incident mattered little in the end, considering everything else that went wrong in the race for the pole-sitter.

"At the time it wasn't frustrating, because I didn't know," the 31-year-old said. "It felt like I was sitting there forever.

"Now in hindsight, not that frustrating either, because there were so many things went wrong today, and that was one more small thing, which actually didn't make a difference in the end.

"I wouldn't have been able to get the Red Bulls anyway, because they were on the supersofts, and they lasted pretty well in that stint, so that didn't make a difference."

Rosberg now trails Hamilton by 19 points in the Formula One drivers' standings, having held a 43-point gap over the Briton earlier in the season.