Central Coast skipper John Hutchinson has conceded the loss of senior talent will make it tough to defend their A-League title, but has put his faith in the emerging younger ranks as the team kicks off its pre-season tour of Indonesia.
Coach Graham Arnold has been rebuilding his squad after losing the likes of Bernie Ibini (Shanghai East Asia), Mathew Ryan (Club Brugge), Oliver Bozanic (Luzern) and Pedj Bojic (Sydney FC) in the off-season.
The A-League champions will also start without two key veterans - retired defender Patrick Zwaanswijk and striker Daniel McBreen, who's on loan with Chinese club Shanghai East Asia until November.
"Obviously it's going to be a tough task this year with the quality we've lost," Hutchinson told AAP from Bandung, West Java, where the squad have spent the past three days training for Friday's opening Menpora Cup clash with 2012 Indonesian Super League victors Sriwijaya FC.
"A lot of players have left. A lot of quality has left.
"But we've got a lot of new young boys to look out for, Mitchell Duke, (Zachary) Anderson, (Trent) Sainsbury.
"They are gelling very well into our system and hopefully they're ready to go."
Ambitious 22-year-old target man Duke, who was named in the Socceroos squad for September's friendly against Brazil, has been in scintillating form and will present stiff competition for prodigal son Matt Simon for the starting striker spot.
Simon spent an injury-plagued year with Korean side Chunnam Dragons, but before his departure racked up 40 goals from 124 games for the Gosford-based club.
"We'll also have Daniel McBreen coming back from his loan in November, and Mile Sterjovski as well for No.9," said Hutchinson.
"So really we've got four players for one position, but you need that competition if you're going to do well on the field as well."
Hutchinson is one of only two foundation players left at the Mariners, along with forward Adam Kwasnik.
Since taking up the coaching position in 2010, Arnold has focused on transitioning teenage home-grown talent into the senior squad.
He recently signed 15-year-old Anthony Khalik - the youngest player ever to be on the books of an A-League squad - and 16-year-old Tom Slater, the son of former Socceroo Robbie Slater.
The Mariners arrived in Indonesia on Monday in preparation for the competition, which includes group matches against Malaysia's under-23 side Harimau Muda and local Super League club Persib Bandung.
"The challenge of playing against the unknown is what we're looking for," Arnold said.
"We've got three games in five days and we've got 19 players here to give everyone the opportunity to get 90 minutes into their legs.
"By the time we get back home ... we'll be ready for the first game against Western Sydney."