The Villa full back, who qualifies for Poland through his mother, has started every game for Poland at the World Cup as they progressed through the group stages.
They faced Argentina and Lionel Messi in their final group game last week - before going up against world champions France on Sunday.
They were beaten 3-1 by Les Bleus but for Cash, who went up against Messi and superstar Kylian Mbappe in the space of four days has described the surreal experience of facing the pair and playing at a World Cup.
He revealed that against Mbappe, who has been in red hot form in Qatar, he felt like his legs were burning.
He told the Guardian: "I spent the afternoon watching his clips and I knew it was going to be a tough test, but when he gets the ball, stops and moves, he’s the quickest thing I’ve ever seen.
“I said to him at the end: ‘Can I have your shirt?’ and he gave me his match-worn shirt so I’m delighted with that.
“I’m watching the videos while lying in bed. In real life he’s burning my legs –that’s the difference. It’s a massive difference. When he stands you up and moves he does it really well. He drops the shoulder, goes short then long. I got into a couple of races with him and I did all right. You look over your shoulder and he’s there.
"I didn’t know whether to drop off or go tight and when I went tight he just spun in behind. I did everything I could.
“When it was one v one I thought I’d done OK against him, he didn’t really run me once. There were times where he got space on the counterattack, which is where he scored the second goal, and that’s where he hurts teams.”
“Playing against Messi and Mbappé in the space of four days is a learning curve.
"It’s a boy’s dream to play in a major tournament against these types of players, and to get their shirts.”
Cash managed to bag Messi's shirt thanks to Villa team mate and Argentina goalkeeper Emi Martinez - as well as Mbappe's match jersey.
Now he is heading home to re-join his Villa team mates following a memorable first international tournament - with France and Mbappe getting ready to face England.
And asked if he had any tips for England right back Kyle Walker ahead of the last eight clash, Cash said: “They don’t need any tips.
"They’ve got Kyle Walker who can play right-back and he’s probably just as quick as Mbappé.
"He knows Mbappé is amazing but Kyle is England’s best right-back. So if anyone’s going to stop Mbappé, Kyle is the man to stop him. I said before that [Raheem] Sterling was my toughest opponent – when we faced Manchester City, he was brilliant. Sterling’s rapid, but Mbappé is electric.”