An assistant referee was struck by a firework thrown from a section of Tottenham supporters during the London side's Barclays Premier League game at Aston Villa.
David Bryan, who was running the line in front of the Spurs fans located in the Doug Ellis Stand, was hit by a flare or smoke bomb thrown after Andros Townsend opened the scoring in the first half.
The restart after the 31st-minute goal was delayed after the incident but Bryan, who appeared to have been hit on the back of the neck, was fit to continue.
The Football Association and the Premier League, who have issued warnings about flares this season, are likely to investigate.
The incident was captured by a television camera.
A fan was led out of the stadium by police and stewards soon afterwards.