Arsenal manager Arsene Wenger insisted he would never take a risk with a player's life after goalkeeper Wojciech Szczesny suffered a head injury at Manchester United.
The 23-year-old Poland international did not immediately move after hitting the ground following the aerial collision but was soon deemed fit to continue by the club's medical staff.
Wenger said: "I listen to the doctor. If he says to me he has to come off, he comes off.
"No matter if we have seven men on the field, I do it.
"You have only one life and you have 60 games per year."
When asked if the doctor had told him Szczesny was fit, Wenger, speaking in his post-match press conference, said: "No, nobody told me anything about him.
"If he said there was a problem I would have taken him off."
Vidic was taken to hospital after his head took a heavy blow in hitting the hip of airborne United keeper De Gea.
Although a stretcher was not used, Vidic appeared shaken and was taken off the field following the clash late in the first half and did not return after the break.
Moyes said: "I hadn't seen the incident from the touchline but I have had a chance to see it (now).
"It's quite a horrific looking one. As far as I know he is okay.
"He is conscious, we will get a scan, but as far as we know, we hope he is going to be okay."
The charity Headway, which aims to increase awareness of brain injury and its consequences, made headlines last week when they criticised Spurs' actions following the Lloris injury.
When asked about the latest two incidents, spokesperson Luke Griggs told Press Association Sport: "I don't want to get involved in judging the decision of Szczesny - every situation is unique and different and the medical team have made a call.
"With Vidic, they have taken him off after the medical team deemed him not fit to continue. He was unsteady on his feet, there were more obvious signs."
Since Headway spoke out last week, there have been widespread calls for stronger protocols concerning on-field incidences of concussion.
Griggs said: "From the very start the whole situation was to raise awareness about head injuries.
"It has made people think. Especially the impact it has on youth and amateur football, about taking risks when they are playing football.
"They might want to be a hero and carry on - and they don't have medical teams at amateur football.
"If they are unsure and unsteady on their feet, it is best to go off."
Lloris, meanwhile, was left out of the side for Spurs' defeat to Newcastle by Villas-Boas.
Villas-Boas claimed the 26-year-old looked "ready to play" but he failed to come through a post-concussion assessment carried out on Saturday adequately.
The Portuguese said: "The medical department felt that it was a bit too soon.
"Probably had the game been on Monday, he would have played. I expect he will play for France (in the World Cup play-offs).
"For them, it was a bit too soon although clinically and medically all the signs were that the player was ready to play."
Lloris briefly lost consciousness after his collision with Romelu Lukaku at Goodison Park but insisted he was fit to continue after coming round.
Villas-Boas then decided against making a substitution and he continues to insist that was not the wrong decision despite Lloris' latest unavailability.
He said: "No, not in my opinion, sorry.
"Nothing has come to light, the player is absolutely fine."
A statement from Wayne Diesel, the club's head of medical services, read: "We've continued to monitor Hugo all week and after discussions, Andre and the medical department have agreed to afford the player a couple more days' rest.
"Hugo is naturally disappointed as he was keen to return to action however we feel this decision is in the player's best interest."