Thirty odd years ago, I was in the U.K. at the time, I had a slim collection of short SF stories which I'm trying to identify. The cover I dimly remember as an abstract image, like a close up of a Pollock or perhaps a lava lamp. It was not a new book then.
It included a story about a long time 20th century junkie whose search for an elusive 'ultimate high' brings him to a mysterious drug pusher. The pusher is revealed to be an alien talent scout for a gladiator school on a different planet. The junkie enlists and fights in the games, the other combatants (mostly non-human) are collected down-and-outs too and also alien to the planet.
There is perhaps a rebellion (?) and a downer of a return to earth.
Any ideas on the title of the short story or the collection?