Investigation into the flare that struck assistant referee David Bryan at Villa Park on Sunday will be launched by the The Football Association.
Bryan was hit on the back of the head by the flare, which was thrown from the section of the ground allocated to Tottenham fans.
The incident occurred just after Andros Townsend had given Tottenham a 1-0 lead over Aston Villa in a Premier League game that saw the London club go on to win 2-0.
An FA spokesman said: “The FA will investigate this matter, which is unacceptable.
“We will await the match officials’ report and will be speaking to the clubs.
“Such incidents highlight the dangers of pyrotechnics being used in a football stadium.”
Meanwhile, West Midlands Police have arrested two men, aged 25 and 47, and the FA will await a report from the match officials before deciding what action to take.