Stajcic said United, who were fourth at the start of this round, had some of the most skilful players in the competition but the Victorians could be vulnerable in Gosford on Sunday.

"They're a very experienced team, a very technical team but they've also got a few vulnerabilities which Newcastle exploited last week," Stajic said, referring to United's 1-0 home loss to the Jets.

"It's going to be an interesting matchup for us and certainly a good test of how we're travelling and how we're progressing."

Stajcic spent some of this week addressing the Mariners own flaws after they conceded three first-half goals in a 3-1 home loss to Adelaide United which left them languishing in 10th spot.

"From the 20th minute to the 70th minute it's probably the poorest football we've played this season," he said.

"The positive signs were we started well and ended well but the sandwich in the middle wasn't very good at all and certainly our defending during that period let us down."

Defender Kye Rowles returns from Olyroos duty to shore up that unit while Stajcic also has midfielder Daniel De Silva making his comeback from a knee injury.

"The squad depth is the most we've had all year this week which is every coach's dream," he said.

"You want to have tough selection (decisions) for the game."

There could possibly be a Mariners debut for former Newcastle Jets forward Jair, although he is recovering from a quadriceps strain.

"He's still not 100 per cent fit, so we'll see if he takes a spot on the bench," Stajcic said.

He confirmed Serbian midfielder and leading goalscorer Milan Duric would miss the match due to a hip injury.

Australian Associated Press