His manager Xabi Alonso said: "It was a concussion, but beyond that I do not know. I have only seen one clip of the incident, so we need to wait. What we know is that he left the stadium conscious and is now in hospital undergoing precautionary tests.

"We need to wait. Hopefully it will not be too serious, but at the moment we just have to wait."

According to Argentine journalist Gaston Edul, Martinez is staying in hospital overnight. But the keeper is said to be conscious and doing well. Scans on his head, back and neck have come back all clear but he has a bone injury in his jaw.

The incident has cast doubt on Martinez's availability for Chelsea's next three matches, at home to Tottenham in the Premier League, away to Liverpool in the Carabao Cup and at home to Manchester United in the league.

Concussion protocols will need to be followed by the London club, which mean Martinez must come through a six-stage 'return to play' procedure before he can return.

Pedro Neto scored a brace at the Hill Dickinson Stadium as Chelsea ended Everton's unbeaten start to the season. The Blues kept their first clean sheet in the Premier League for nine months in the process.

Matchwinner Neto told TNT Sports post-game: "We are really pleased. Shame for Emi but we wish him all the best. This win is for him. We are really happy but of course are thoughts are with him.

"Happy to get the win. We needed a clean sheet to be honest. We did a very good game. Emi deserved this. Mike deserved this as well. So we are really happy."

"We looked in control of the game, there were moments for sure when we had to defend, especially in the first half, but overall the team looked mature, knew what to do in each moment, and knew we’d have our own moment. That happened in the second half.

"After that, we were good with the ball, creating chances and not conceding much. To win away is always tough, and we got the clean sheet. We knew it was a matter of time and finally we got it."