LONDON (REUTERS) - Manchester United manager Louis van Gaal has been refereeing training games to help his players keep their emotions in check for the Premier League top-four showdown with Liverpool at Anfield on Sunday.

The Dutchman has a reputation as a disciplinarian who keeps his players on a tight leash but has seen emotions boil over in big games this season with Chris Smalling sent off against Manchester City and Angel Di Maria seeing red against Arsenal in the FA Cup.

With Anfield proving a traditionally hostile environment for visiting United sides and only two points separating the teams in the battle for a top-four finish, Van Gaal was keen to lay down the law.

"I have been the referee on the training pitch and I have whistled when they have to control their aggression, for example, to prepare already for the atmosphere," the Dutchman told reporters on Friday.

"Control of emotion is also a talent."

The United boss has been heavily criticised for his side's frequently negative playing style this season, but there were few complaints after last weekend's emphatic 3-0 win over Tottenham Hotspur.

For all the talk of long-ball tactics and a move away from United's traditions of attacking football, Van Gaal seems to have stumbled across a formula that could yet appease the purists.

Despite still focusing heavily on the ruggedly physical attributes of Marouane Fellaini, there was plenty of attacking verve on show against Spurs.

Yet it will count for nothing, Van Gaal said, unless they can build on that performance at Anfield.

"I think we played very good in the first half - it was also good to have an evolution that is very positive," he said.

"(But) it says nothing when you lose the next match. Liverpool is not a ground where Manchester United have won a lot.

"When we have won at Liverpool, that will have shown we have improved further."

Both teams come into the game in superb form with Liverpool having won five league games in a row and eight of their last nine while United have won three in succession and are undefeated in 17 of their last 19.

With United desperate to keep their noses ahead in the top-four battle, Van Gaal described it as a game they dare not lose.

"I want to win against them again. It's very important," he said. "I think every player knows the importance of this game. We are in a very crucial stage and cannot lose."