The young forward had provided some of the few bright moments in attack as the Reds were locked at 0-0 with the visitors, who would go on to win the game with Joao Moutinho's late strike.
Although displaying some neat touches and showing confidence in possession, he was the man to make way when Bruno Fernandes was introduced and Ralf has outlined why that was the case.
It came down to whether Greenwood or Edinson Cavani, who claimed the equaliser at Newcastle United recently, would make way for the creative talents of Bruno.
“The question was shall I take off Mason or shall I take off Edi," said Rangnick.