Reflecting on Fernandes' conduct during Manchester United’s historic 7-0 loss to Liverpool, Souness pointed out how he appeared to give up, walking around the pitch, pointing fingers, and showing visible frustration.
"I will never get the image out of my head of how he reacted to going three goals down at Liverpool when Manchester United lost 7-0 at Anfield," he said.
"He just threw the towel in, walking around pointing fingers at his teammates, shrugging shoulders. For the oldies that read this, I will quote the Billy Ocean song: 'When the going gets tough, the tough get going.' But Fernandes doesn't.
"His actions at Anfield showed me where his mental toughness was, nowhere. And that's my point, just having ability isn't enough to be a top player, he needs to show mental toughness, discipline and workrate when you're up against it and that's certainly what United are at the moment."