Johnson said he felt no sympathy for Cook.
"I don't think I'm going to feel sorry for an opposition player," he said. "We all go through our highs and lows and I understand that and have been through it just like any other cricketer.
"It's definitely very tough for him at the moment. Obviously everyone looks up to their captain so I'm sure he's finding it very hard at the moment.
"There's a lot of pressure on him and he's definitely feeling it."
