However, the 23-year-old has now regained full fitness and is looking to prove his worth on the tour down under in July.
"The hamstring feels really good, it feels fantastic," Gray told Sky Sports News. "At the time, I knew right away something had gone and it tore.
"I suppose on the grand scale of things it's not too bad an injury to pick up. The timing wasn't great, but it hasn't kept me out too long. It has been a challenging season personally, as things haven't quite gone to plan.
"Just before the injury I started to get a bit of consistency back. I was happy with the way I was playing during the Six Nations. This season will have been a huge learning curve for me. It's something I will learn from and look back on in future times as I have been able to deal with the problems."
Gray will leave current club Sale Sharks to play in France for Castres next season.