The sight of Charles Leclerc's Sauber spinning into the gravel in Friday's initial session led to the red flags coming out, and Vettel was deemed not to have decelerated enough when the stewards reviewed the incident at the end of the session.
Vettel needs to finish within eight points of title rival Lewis Hamilton to keep his championship hopes alive for another round and a three-place penalty would create another obstacle for the Ferrari driver, who has struggled to match Hamilton for pace at the last four rounds.
The German struggled through a hard day of slithering in the rain and then picked up a potentially fatal grid penalty for speeding under red flags during the morning session.
"If a driver commits a crime like that, speeding under a red flag, the biggest thing that will hurt a driver is to fine him".
The stewards, having viewed the relevant video evidence, positioning data and telemetry, and heard from a team representative, found that Vettel failed to stay above the minimum time set by the FIA ECU in marshalling sectors 6 and 7.
Taking their time to make a decision, especially when factoring in the extreme wet conditions in which the first practice session had taken place, the stewards eventually decided that they had no choice but to issue the same punishment to championship chasing Vettel as they had previously to Ricciardo and Ocon.
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In the bottom of the 10th inning, Machado ran out a ground ball to shortstop (something he doesn't, admittedly, often do) when chaos ensued.
"I saw the red flag and slowed down, had a look around to see if there was a auto potentially stuck in the wall or if there was one around Turn 9 or 10 and then slowed down significantly to comply with the rules".
Vettel may face a three-place grid penalty for Sunday's race if he is penalised in the same way as two previous drivers for the same offence this season.
"[For example] if you're halfway through Turns 17 and 18 [the fast double-right hander] it's a bit tricky to slow down as much as you should".
"But there have been many - or several - times that I've been in the firing range and Seb's always been really respectful and supported me, so I thought it was only just to do the same". "Lining out 27.7 seconds precisely, as not complying with the rules, I think is wrong".
"I think the respect between us has always been there despite the fact that maybe we are very different". "They found it took too long". I think it's a mutual respect that we have for each other. I should have slowed to 30kph but then maybe a auto behind me would have crashed into me, and what's the point of that?
His penalty followed two similar examples.