The 32 year-old former paramedic, who arrived in New Zealand as a backpacker, has had his contract with the A-League club terminated by mutual consent.
Riera, who played 68 times for the Phoenix, turned down the final year of his contract after he decided the rigours of day-to-day training was no longer for him.
The one-time A-League All Stars representative said he had been considering his decision since the final game of the season.
“It was a very hard decision to make but I had been thinking about it for seven months,” Riera said.
“I’ve had a few injuries lately and as you get older it becomes harder to shake them off.
“It has nothing to do with money; it is a very personal thing and it was difficult to tell Ernie what I wanted to do.
“Ernie has always been honest with me and I had to be honest with him.
Merrick said the news was a big surprise.
“Albert was a pleasure to coach and I am so pleased we had that friendly game at Auckland City where I first saw him,” Merrick said.
“He slotted straight in and was our player of the year in his first season.
“You really have to respect and admire what he did late in his career.
“Signing Albert was one of my best decisions in football.”
