Sydney FC coach Graham Arnold says coaching Wellington Phoenix is the hardest job in the Hyundai A-League and paid tribute to departing coach Ernie Merrick, who resigned this morning.

Speaking at the Sky Blues’ recovery on Monday morning, Arnold spoke in glowing terms about Merrick, a former A-League Championship winner with Melbourne Victory.

And he spoke about the huge difficulties in managing a club like Phoenix.

“I just heard and it’s sad. Ernie’s the most successful coach in the A-League in terms of trophies and games," Arnold told reporters.

“For me he was always a fantastic guy and a fantastic coach. For him to resign, obviously is probably family related as well because he would’ve spent a lot of time away from his family.

Phoenix bombshell: Merrick resigns as coach

“I tell, it’s gotta be the hardest job in the A-League. The travel is very difficult, and having to deal with the international FIFA windows losing players.

“That’s what people don’t understand. The first eight or nine games he’s lost players twice and they’ve had to travel back from the US, then they are fatigued, then you lose a game or two and it rattles players’ confidence and it’s hard to bring everything back together.”

Arnold added the times he’s seen Phoenix play this season, he’s been impressed.

“Every game is tough in the A-League but they have the players as Ernie has recruited well and they were good when I saw them,” he added.

Social media had its say on the shock resignation this morning, some drawing parallels with the shock resignation of New Zealand PM John Key on the same morning.