Is the guard of honour compulsory?

To begin with, what is a guard of honour? The tradition is a mark of respect for an opponent that has already won the title prior to a specific fixture, and manifests itself as two lines of players from the opposing side clapping the title winners on at the start of the game.

The guard of honour was performed as far back as 1955, when Manchester United clapped Chelsea onto the pitch. United then continued the tradition in 1991, honouring Arsenal's title win at Highbury. 

However, it is by no means compulsory, and players cannot be forced to do it if they do not want to. The gesture is organised prior to the game between the two clubs.

The tradition has continued during the last few decades, with a notable recent example being in 2012/13 when Arsenal reluctantly clapped the traitorous Robin Van Persie onto the pitch as his new team United strolled to the title.

Chelsea were honoured last season by Watford, with the retirement of John Terry elevating the ceremony even further. The ball was kicked out in the 26th minute, to represent Terry's number 26 shirt, and the veteran defender was then substituted off to a round of applause from the stadium.

There has recently been some controversy over Zinedine Zidane saying that he would refuse to give Barcelona a guard of honour if Real's rivals secure the title in the game previous to next month's El Clasico. Barcelona famously honoured Real in 2008 at the Bernabeu, however earlier this season they refused to perform the gesture after Madrid had won the FIFA Club World Cup, which is Zidane's reasoning for saying he wouldn't give Barca the satisfaction.