Arsenal have been urged by concussion campaigners to be cautious with Hector Bellerin after his head injury against Chelsea.
Bellerin took an elbow to the face from Marcos Alonso as the Chelsea player headed in the opening goal of the Blues' 3-1 victory over Arsenal on Saturday and then landed hard on the pitch. He was immediately substituted and Arsenal boss Arsene Wenger said the right-back had not known the score of the game after the incident.
Football Association regulations say Bellerin can return to training on Friday if cleared by doctors, meaning he could be fit to face Hull City on Saturday.
But Dawn Astle, whose father Jeff Astle died from brain trauma that doctors said was caused by heading footballs, told the Daily Mail that Arsenal need to be careful not to rush him back too soon.
"There is no room for error," she said. "There is no room for risks. No risks should be taken at all. It's better to err on the side of caution.
"I've watched the clip again. He's just out. People think of concussion, it is a bit of a wishy-washy word, but it is a brain injury.
"If his arm had been broken, people can see that. But you can't see what's happening to the most fragile, complex organ in the body that once it is damaged doesn't repair itself. It's so important."
Arsenal said Wednesday that no decision has been made on when Bellerin will return, but that he has passed every medical test so far.
"Our Spanish right-back is now in the final stages of the FA return to play protocol for concussion. He has had daily assessments and successfully completed each step of the graded progression so far," Arsenal said in a statement.
"Hector will be further assessed on Thursday and Friday, prior to a final decision being made regarding his availability for full training and Saturday's home match against Hull City."
Bellerin was able to watch the second half of Saturday's game from the Arsenal bench and his recovery is being overseen by club doctor Gary O'Driscoll, who formerly worked with Ireland's national rugby team and is the son of Barry O'Driscoll, the former World Rugby medical adviser who has campaigned for greater care when it comes to concussion.
Even if Bellerin is declared fit for the Hull game, Arsenal could choose to rest him ahead of the trip to Bayern Munich in the Champions League next Wednesday.
Headway, a charity dedicated to brain injuries, praised Arsenal for removing Bellerin off the pitch immediately but also said a "safety-first approach" should be taken going forward.
"We were pleased to see that after concussion was suspected, the protocol was followed and the player was removed from play," Headway said in a statement.
"Quite rightly, it appears he is going through the graduated return to play protocol. While this normally takes 14 days, the FA's rules state that if the player is in an enhanced care setting and as long as they pass all the necessary tests, they can return after six days.
"If the player shows any signs or symptoms of concussion during this time, they will have to begin the process again.
"Of course, regardless of how many days have passed, we would always advise the safety-first approach and recommend players do not return to play unless they are medically assessed as being fully fit to do so."