Wellington Phoenix midfielder Adrian Caceres will miss Sunday's knockout semi-final against the Newcastle Jets.

The 28-year old will return to his homeland of Argentina to be with his wife Romina or the impending birth of their first child.

Complications arising from the pregnancy indicate that Caceres will not be back in time to take his part in the Phoenix's biggest clash in their short history.

"At this stage it's touch and go," said assistant coach Luciano Trani of Caceres' availability.

"It's unfortunate because Adrian Caceres has done a fantastic job when he's come onto the park and he's given us that extra injection of speed and quality that has just given the team the extra boost."