Erling Haaland was in top form in Dortmund's last game of the season.The Norwegian striker was in the starling lineup for Dortmund's Bundesliga clash against Leverkusen on Saturday afternoon.It didn't take long for Haaland to get on the scoresheet.The 20-year-old broke the deadlock after just five minutes as he fired a fierce left-footed strike past Lukáš Hrádecký.Haaland would score again late on as he rounded the Finnish goalkeeper before putting the ball into the empty net.That means Haaland finishes the season with 41 goals in 41 games. What an incredible campaign it has been for the youngster.Erling Haaland during Dortmund vs LeverkusenAfter a dominant performance, Haaland showed his class after the final whistle.The referee for the game, Manuel Gräfe, has been refereeing in the Bundesliga for 17 years.The game between Dortmund and Leverkusen will probably be his last ever match as a referee in Germany's top tier.Haaland showed respect for Grafe by swapping shirts with him after the game.Watch the moment below:

Haaland then posed for pictures with Grafe and the other officials. What a great gesture from the youngster.

Grafe is one of the league's best referees but the current rules mean he can no longer officiate in the league. 

Read More - Erling Haaland: Latest transfer rumours, news, gossip and more

The referee turned 47 last September. The Bundesliga states that their officials can't be over the age of 47.

Dortmund sports director, Michael Zorc, criticised the rules before the game.

The Football Terrace: Championship star 'is the right player for Arsenal' - Do you agree?

"As of now, Manuel Gräfe will play his last game as a referee at Signal Iduna Park tomorrow," he said, per Kicker.

"We will of course say goodbye to him, as it should be. But I am happy to join the large crowd of managers, coaches, players and fans. who would like to ask the DFB to reflect on their own actions.

"That one of the most respected referees in Germany is only sent into forced retirement against the resistance of the masses because his age switches from 47 to 48 sometime at midnight me for not being very professional.

"It's actually a joke. There are no young and old players, there are only good and bad. And it is the same with the referees."