The Australian Cricketers' Association (ACA) has condemned sections of the Lord's crowd for jeering Steve Smith after the batsman sustained a blow to the neck in the second Ashes Test.

Having already taken a hit to his forearm which required treatment, Smith was forced to retire hurt when a short ball from Jofra Archer thumped into him just below the helmet.

Australia's former captain was clearly frustrated at having to cut short his innings on medical advice, though he came back out to bat later in the session. He was eventually dismissed by Chris Woakes for 92 as the visitors reached 250 all out in their first innings.

The 30-year-old was, in the main, warmly received when he left the pitch and also as he made his way back out to bat, though some boos could be heard on his return to the middle.

Smith, along with team-mates Cameron Bancroft and David Warner, has been booed by sections of the crowd during the ongoing Ashes series following the trio's involvement in the 2018 ball-tampering scandal.

The ACA, however, has criticised the behaviour in the case of Smith's injury, while also praising the protocols followed by Australia's medical staff.

"The overnight events at Lord's show the importance of the concussion protocols which have been developed in Australia over the last few years," a joint statement from ACA president Greg Dyer and chief executive officer Alistair Nicholson said.

"Administrators in Australia working with the ACA and now the ICC have done a good job in putting the protocols in place. Plainly, they are necessary to protect the players who are struck.

"This is a workplace for these players. The reality is that cricket can be a dangerous sport, especially when the bowling is as ferocious as it has been in this series.

"To see the protocols practiced at Lord's overnight was important and correct. What was unwelcome and incorrect was the sound of booing of an injured player.

"Cricket deserves much better than that. And Lord's, the home of cricket, deserves much better than that also. What we witnessed was bravery from an outstanding young man. It should be commended not vilified.

"Over the English summer, generally the crowds have been terrific and really added to the contest. But when someone is hurt, yet the boos continue, it's time to call 'enough'.

"At any rate, the players have already served the toughest penalties in the history of cricket. Surely it is time to move forward."

Smith's injury prompted immediate concern, with Australia coach Justin Langer acknowledging the incident brought back painful memories of Phillip Hughes' death.

"You never like seeing your players get hit like that," Langer told a news conference. "There's obviously some pretty rough memories of a blow like that. So there's no fun in it."

Australia opener Hughes died after being struck on the back of his neck during a Sheffield Shield game in November 2014.