It was believed that Priestland would be out for nine months but he returned to take on Cardiff Blues in April.
But as Priestland was warming up for Scarlets' RaboDirect PRO12 semi-final clash with UIster, disaster struck as his Achilles injury flared up and he was forced to sit out the 28-17 defeat.
Priestland had been named in Wales' 32-man training squad for the two-Test tour of Japan in June, the 26-year-old hoping to make up for lost time having missed out on the 2013 Six Nations.
But that chance has been taken away from him with his latest injury setback, Cardiff Blues' Rhys Patchell being called up as his replacement, and Priestland insists it is a big blow.
"I thought everything was fine with my Achilles but it's a part of rugby," he said.
"I was pretty low over the weekend and I'm still coming to terms with it. It's a shame because I felt really good and my body has been really good but I'm sure this extra break will make things better in the long term.
"It literally happened at the end of the warm-up with five minutes to go until kick-off.
"To be so close to actually making it on the field and hitting the target I had set myself was a pretty devastating blow.
"There's no real rush to come back for anything so I'll just make sure everything is right and ready to go for the start of next season.
"I'm sure everything will be fine way before that. It's a bit of a shame because I felt really good and my body has been really good but I'm sure this extra break will make things better in the long term."
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