The 20-year-old has been described as a player with a bright future by manager Steve Bruce.
And with former keeper Sam Johnstone having now left The Hawthorns, Griffiths had been tipped to compete with David Button and Alex Palmer for the number one jersey next season.
Instead, though, Albion have allowed him to continue his development at League One Portsmouth – with Griffiths having previously enjoyed successful loans with Cheltenham and Lincoln.
The Baggies, though, have insisted on a 24 hour recall in case either Button or Palmer get injured.
That clause is possible because Ted Cann – who has become number three following Griffiths’s move to Fratton Park – hasn’t played five professional games.
The clause also means Albion don’t have to enter the market for another keeper this summer.
There has been speculation Ben Foster could return to the club after he spent time training with the academy. But that was just a favour to help the 39-year-old stay fit.
“We’ve got an instant recall if something happens back here,” Bruce on Griffiths’s move.
“I wanted him to go out. That was always in my mind with a young one. It’d be unwise of us to not let him play. The more he plays, the better.
“We have the instant recall which is vitally important, because we’re not at any risk. I’m really, really pleased with our goalkeeping situation.
“We know Griffiths is a very, very good goalkeeper and we don’t want to stop that progress.
“Portsmouth will be a good test for him.”