Arsene Wenger says a concussed Hector Bellerin had no idea Chelsea took a 13th-minute lead in the Premier League leaders' 3-1 win over Arsenal.
Gunners boss Wenger felt Marcos Alonso's aerial challenge on Bellerin constituted dangerous play as the wing-back arrived at pace and caught the Spain international with his arm as he headed home.
Bellerin made way on medical advice shortly afterwards and second-half goals from Eden Hazard and Cesc Fabregas effectively ended Arsenal's title ambitions.
After telling a post-match news conference his right-back was concussed, Wenger said: "Was he completely knocked out… He didn’t know the result of the game at the time. He didn't see the goal.
"The decision [to substitute Bellerin] was, for me, very quick, but we have to respect that. It is the head."
Wenger believes players not receiving adequate protection from officials in aerial challenges is something that needs to be addressed.
"One of the particularities of the game today is that referees are much more severe with tackles on the ground and let much more go with elbows in the face," he said.
"It is not only today but in many, many games I see that. But it is more dangerous to hit the head than the legs."
Arsenal are now 12 points behind Antonio Conte's runaway leaders, concluding a damaging week in which they also suffered a shock 2-1 home loss against Watford.
On both occasions, Wenger watched from the stands as part of his punishment for pushing the fourth official during last month's match versus Burnley.
"It is very frustrating because I cannot do my job like I want to do it," he said.
"But I have to pay for what I did. I accepted it and we have to get on with it – I especially have to get on with it.
"It is frustrating to watch from upstairs because you sit in the middle of people. They call on the phone, stand up, get down.
"I don't think, as well, that is an explanation of our defeat."