Vettel was third fastest in practice ahead of his home Grand Prix [GALLO/GETTY]

Defending world champion Sebastian Vettel singled out Ferrari as presenting the main threat to his Red Bull team in this weekend's German Grand Prix.

After seeing his teammate Mark Webber top the times in Friday afternoon's free practice session ahead of Ferrari's Fernando Alonso, the third-placed home hero said it was "a good thing" to see the Italian constructors doing well.

"I think Ferrari again looks a bit competitive after what we have seen today with both cars," he said.

The runaway leader of this year's title race added that it was difficult to make too many judgements so early in the weekend at a circuit, set in the Eifel mountains, where the weather was infamously capricious.

He said: "McLaren was very difficult to judge if they are back to where they were for the majority of the season, in terms of exhaust and blowing so we will see.

"They will be quick again tomorrow, so you cannot forget about them.

"But I think if we can make a step forward then it is worth a lot. We don't know the conditions for tomorrow and Sunday yet.

"Rain is forecast – it is on the way. So, it is a question or when and where it will hit us. Now we need to sit down and see what we can improve, but surely there is room to improve."

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By his own consistently high standards this season, Vettel may be facing a slight blip in his own performances after clocking only the third best time and could, on Sunday, face starting on the second row of the grid, or worse, for the first time this year.

In nine Grands Prix so far this season, he has qualified on pole seven times and twice in second place, but both of those lesser results have come in the last five races.

He has also won only once in his last three outings – though both other races saw him finish second – after winning five of the opening six races.

But with a lead of 80 points ahead of Webber and 92 on Alonso, Vettel knows it would take an extraordinary change of form and fortunes for him to fail to win his second title.

Webber, however, plans to maintain as much pressure on his team-mate as he can especially after being told that he remains free to race as hard as he likes against him, following the team orders controversy at Silverstone two weekends ago.

"It's all the fine margins I keep talking about - get the start, first stint and build it up," he said.

"My race at Silverstone wasn't too bad, but Fernando drove a very good race and Seb and I were pretty close. To beat everyone on the day, you have to get everything right and I hope to do that on Sunday."

Source: AFP