Walter Mazzarri has warned his Watford defenders that they face a "very difficult" task in halting Zlatan Ibrahimovic's impressive scoring run at Manchester United.

The ex-Sweden international has scored five goals in six games for the Red Devils since joining the club as a free agent during the summer, including a consolation strike against rivals Manchester City last time out in the league.

Next on Ibrahimovic's hit list is a Watford side in a confident mood following their first top-flight victory under Mazzarri last weekend, and the Italian coach - who knows the United striker well from his time in Serie A - is anticipating a tough afternoon at the back.

"Ibrahimovic is the type of player I call an eternal player, immortal player. Unfortunately I have played against him many times because he's a great player who can make the difference on the pitch," he told reporters.

"He's very complete as a player. We will try, and I will try, as we always do with the great players in front of us. We can try and limit their capabilities and qualities but it's very difficult to stop them completely, but we will try for sure."

Ibrahimovic fired a blank for United when coming on for the final 30 minutes of Thursday's Europa League defeat to Feyenoord in Rotterdam.