Stewards had 'no choice' but to penalise Sebastian Vettel - Toto Wolff

Ferrari driver Vettel should be lining up alongside title rival Lewis Hamilton at Austin but will instead start fifth after picking up a three-place grid penalty for a red-flag infringement in practice.

Vettel received some sympathy from fellow drivers for the "harsh" penalty, but while Hamilton's team boss Wolff claimed he would prefer to see the protagonists go wheel-to-wheel into the first corner he believes it was right to punish Vettel.

"The stewards have a really tough job because you have rules and you need to be consistent in the rulemaking," said Wolff.

"The rule says you need to reduce speed, do not be above the delta time. If you fail to do so, you're getting a penalty.

"I don't think the stewards have any choice in their decision making.

"From a racing point of view of course you'd like to have the two championship contenders going wheel-to-wheel into the first corner.

"From a racing standpoint this is what I'd like to see.

"But it's very easy to hit out. If you are the police, there are regulations, and you need to act upon them."

Vettel's penalty matches those earned already this season by the likes of Daniel Ricciardo and Esteban Ocon for the same offence.

Wolff's other driver Valtteri Bottas avoided a penalty for a minor infringement in qualifying, when he and Ocon were found to have driven too slowly on their respective in-laps after the final session had ended.

It means polesitter Hamilton, who can claim a fifth title on Sunday if he outscores Vettel by eight points, maintains a three-car buffer between himself and Vettel.

Vettel will need to pass Ricciardo's Red Bull, Bottas and the other Ferrari of Kimi Raikkonen to stay in mathematical title contention should Hamilton take victory.

Wolff said Mercedes may yet implement team orders to seal the championship and he is "still wrestling" with the decision.

"The objective for Valtteri is to really go for it at the beginning," said Wolff. "He hasn't got a lot to lose.

"If at the end we find ourselves in a situation where we again need to evaluate the points we will do that.

"I know from the points we are looking solid but everything can happen in this sport and Ferrari has come back strong, it's what we have expected.

"That's why I'd like to keep all options open."