Brad Friedel believes the authorities are "doing as much as they possibly can" when it comes to treatment of concussions in football.

Questions were raised about the decision to keep Aston Villa goalkeeper Emiliano Martinez on the pitch after he took a blow to the head during the 4-0 defeat to Newcastle United last week.

Martinez was eventually replaced, but it led to the Professional Footballers' Association to call for temporary concussion substitutes to be introduced to the game.

Speaking to Stats Perform, former Villa shot stopper Friedel said the protocol is improving for dealing with such incidents.

"Concussions are tough to detect," he said. "We play without helmets and, of course... Petr Cech did in his career because he had a fractured skull - [but] you don't get into too many clashes [as a goalkeeper].

"If a striker wants to be a little bit naughty on the through balls, they can leave a foot in, but it doesn't happen that often.

"I'm not so sure what more they could do to protect the goalkeeper. I think the more science that comes out with regard to concussions and concussion protocol, the better. Each season they're trying to do as much as they possibly can."

The former United States international explained he had suffered a concussion during his time at Blackburn Rovers.

"I was playing for Blackburn at home against Birmingham. I got knocked out, I think out for about six minutes, and I answered all the questions," he said.

"I don't remember answering them and I carried on playing it. [It was] no fault of the doctors. I passed the protocol at the time and then I went in at half-time, and then they saw that I wasn't on planet Earth, so I didn't play in the second half.

"As a player, your adrenaline takes over you, you just want to stay on the field, and it's a tough one because it's really hard to tell if somebody's concussed in 30 seconds or a minute or a minute and a half.

"I would hate to be in those meetings with the NFL. A concussion technically is when your brain hits one side [of the skull] and then the other. I mean, for every play in the NFL, that must happen to somebody. It's a tough thing to really clamp down on... And I know they're trying to do as much as they possibly can to make it efficient."

Friedel also expressed his disappointment that Steven Gerrard was recently sacked by Villa following a run of poor results.

Gerrard was replaced by Unai Emery after the Midlands club won just two of their first 11 Premier League games of the season (D3 L6), and while Friedel understands the timing, he also believes his former Liverpool team-mate could have turned things around at Villa Park.

"Disappointed that it happened because Stevie's a friend," he said. "Based on the results, [it was] probably the right time, right before World Cup, and then you're going to have [the January] transfer window.

"I would also like to have thought if they kept him that he would have built the club up and gotten them into a mid-table position.

"That's not how football works and it can be ruthless. Being a head coach can be tough sometimes, but I would just say the run of results was the final blow and perhaps that performance and result against Fulham [3-0 loss at Craven Cottage] when the fans started singing against Stevie, that was probably it."