Referee Michael Oliver, pointing to his watch, looked to indicate that goal-line technology had not verified the ball had crossed the line, despite what appeared to be clear evidence on TV replays.

Hawk-Eye issued an apology to "the Premier League, Sheffield United and everyone affected by this incident" in a statement after the game that acknowledged that ball had crossed the line, but said the view of its cameras had been blocked.

"The seven cameras located in the stands around the goal area were significantly occluded by the goalkeeper, defender and goalpost," the statement read. "This level of occlusion has never been seen before in over 9,000 matches that the Hawk-Eye Goal Line Technology system has been in operation."

Hawk-Eye insisted the technology was tested and "functional" throughout the game, in accordance with the laws of the game.

The visitors will feel hard done by but also had goalkeeper Dean Henderson to thank for securing a share of the points in a lively affair on a rainy evening, where both sides showed a lack of match practice.

He made key saves in the second half, first to deny Keinan Davis and then push away a rasping shot from John McGinn on the hour mark as Villa, who lost 4-0 at Leicester City in their last game before the league was suspended on March 9, made six changes to their starting lineup.

A physical second half saw both sides battle hard for a go-ahead goal, but none came and the result leaves Aston Villa on 26 points in the relegation zone and Sheffield United on 44 points in their chase for European football.

"I don't know whether to laugh or cry," Sheffield United manager Chris Wilder said after the game, which was played behind closed doors at Villa Park.

"The feeling at the time by everybody, both sets of players and staff, was that of a goal."

Along with the Black Lives Matter tributes, there was a moment's silence before kickoff in memory of those who died in the COVID-19 health crisis, which included the father of Villa manager Dean Smith.