Arsene Wenger one of world's best coaches: Louis van Gaal

London: Manchester United football club manager Louis van Gaal believes Arsenal boss Arsene Wenger is one of the best coaches in the world, adding that his longevity at Arsenal is a sign of great success.

The Dutchman will lock horns with Wenger as the two teams meet at Old Trafford on Sunday, having guided United to the top of the Premier League after seven games, reports goal.com on Friday.

Van Gaal, was quick to point out that Wenger - who celebrated 19 years as Arsenal manager this week - should be lauded for his longevity in an industry that has become increasingly unstable through his reign.

"I think that he is doing great work. When you can, like Sir Alex Ferguson, stay in a club for such a long time you have to be very good. Otherwise you shall not succeed," Van Gaal said.

"I think Arsene Wenger is one of the best coaches in the world. Sir Alex Ferguson is the best because he won the most titles. It's easy to say criticise him for not winning the league but when you spend such a long time with one club and everybody is satisfied - the fans, the board, the players - then you are very good, believe me," he said.

Wenger is once again under pressure in the Emirates Stadium hotseat, with Tuesday's defeat to Olympiacos leaving Arsenal's hopes of Champions League progression hanging by a thread.