Image: Richarlison joined Watford last summer from Brazilian side Fluminense

Manchester United, Chelsea and Everton are keeping tabs on Watford striker Richarlison.

The Brazilian forward had a terrific start to his first season in the Premier League, scoring five in his first 12 games.

However, his goal drought now stretches back to November and Sky Sports News understands Watford are concerned that the 20-year old is struggling, having played football for 12 months without a break, first for Fluminense in Brazil, and in the Premier League since August.

Richarlison has made 36 appearances for Watford this season, the most recent coming in the 2-1 defeat to Burnley last Saturday.

Chelsea considered signing the Brazilian U20 international last summer, but the chance of regular first-team football under then-manager Marco Silva prompted the move to Vicarage Road.

Sky Sports News believes Watford would only consider offers of around £40m for the striker they secured on a five-year deal for £11.2m.