Williams’ Sargeant was on a flying lap when he encountered Hamilton at turn 11 in the middle of the track.
The American was forced to take evasive action off the track to avoid the slow-moving Mercedes and was left unimpressed over the team radio, saying: "Mate, come on. It's too dangerous.”
Hamilton said over the Mercedes radio that he was unaware that Sargeant was on a lap as he trying to let Carlos Sainz past: "I didn't realise someone was on a lap. I was trying to get out of the way for Sainz and all of a sudden there was a Williams there."
The incident was looked at after the session by the stewards and the seven-time champion was issued with a warning and Mercedes were fined 15,000 euros for their part in the incident.
An official FIA statement said: "Car 2 (Sargeant) had to take evasive action by going off the track to avoid a collision. Had that not been done, there would have been a serious, high speed crash.
"Having listened to the team radio, it was clear to us that the team of Car 44 failed to warn their driver of the fact that Car 2 was arriving on a fast lap. That was a serious failure on the part of the team, particularly given the speeds on this circuit and the nature of turn 11, which is at the end of a series of high speed corners where driver visibility is impaired.
"We therefore issue a warning to the driver and impose a fine of €15,000 to the team."