As Kiwi captain, Mannering was an automatic original selection in the Wayne Bennett-coached World All Stars squad.
"We're all delighted for Simon and Anna," said Vodafone Warriors managing director Jim Doyle.
"I know Simon was looking forward to playing for the All Stars but it's far more important for him to stay at home to be with Anna at this time."
The Herald on Sunday reported last September that 11 of last season's team, including captain Mannering, had recently welcomed or were expecting babies.
Fellow star forward Ryan Hoffman's wife, Melissa, gave birth to a daughter, Mia Grace, in October.
Mia was born in Auckland because her mother was not able to travel back to Australia after the season ended, Hoffman said at the time.
"So we've got a little Kiwi baby."