Merseyside Police are investigating an incident which saw a flare thrown into the Chelsea section during Sunday's match against Liverpool.
Footage on social media showed red smoke coming from the visitors' section at Anfield after Sadio Mane put the Premier League leaders 1-0 up six minutes into the second half.
Chelsea vs Burnley
April 22, 2019, 7:30pm
Sky Sports News understands a young Chelsea fan needed first aid treatment after the flare, which is alleged to have come from the Anfield Road End's upper deck where home supporters are situated, landed in the middle of their section.
A red mist engulfed part of the Chelsea support and it is understood that the young fan was treated after inhaling some of the smoke and feeling unwell.
Social media also showed Chelsea fans attempting to remove the flare from their section towards the pitch.
Mo Salah went on to add a second goal soon after as Liverpool moved back to the top of the table just a couple of hours after being knocked off the summit by Manchester City.
Jurgen Klopp's side have a two-point lead over City but the reigning champions have a game in hand heading into the final month of the season.
Liverpool next take on relegation-threatened Cardiff City but first face a trip to Portugal where they defend a 2-0 Champions League quarter-final lead over Porto.