Cox, who stayed in Australia while his partner gave birth to their child in February, has decided to end his 16-month stint with the Wanderers.

"I had to make a really tough decision about staying here while my partner had a child back in the United Kingdom, which was to be honest the hardest decision my life," Cox said in a statement on Wednesday.

"I thought we would be able to get through to the end of the season and possibly finals but that is now not possible.

"The last few weeks have been really tough.

"I sat down with the manager and we came to the decision that it's now time for me to say goodbye."

Cox, capped 30 times for the Republic of Ireland, joined Western Sydney in January last year.

Western Sydney's Welsh-born coach Carl Robinson said he understood Cox's decision.

"Having my own family currently spread across the world, I understand and relate to what Simon has been going through over the last couple of months," Robinson said.

."I would like to thank Simon for his professionalism and sacrifice made to the club over the last four months."

Australian Associated Press