Ighalo, 27, joined the Hornets in 2014 from Italian side Udinese and helped Watford win promotion to the Premier League in the 2014-15 campaign.

He scored 15 top-flight goals in 2015-16, but has only one Premier League goal this season and has gone 15 games without scoring in all competitions.

Watford are 14th in the Premier League, eight points above the relegation zone.

During his time with the Hornets, Ighalo played 100 times in all competitions and scored 39 goals.

In the calendar year of 2015, he scored 30 goals in 38 games. He has netted six times since.

This month, Watford have signed two attacking players - AC Milan striker M'Baye Niang, 22, on loan until the end of the season and Argentine forward Mauro Zarate, 29, on a permanent deal from Fiorentina.

Walter Mazzarri's Watford side were shock 2-1 away winners at Arsenal in the Premier League on Tuesday.