The Mariners play the Glory for the third time this season after coming away with a 3-3 draw in the opening round before a 2-0 win at home in November.

Castro only managed 17 minutes in the 2-0 loss after tearing his hamstring.

Okon was exercising caution in dealing with the Spaniard.

“He is (quality). That’s why he was the Johnny Warren medallist last season and probably a big favourite to take it out again,” Okon said.

“I think for the A-League, it’s great to have a player like Castro in our country playing. From us tomorrow, we are aware of how dangerous he is. We need to limit the supply to him and make sure he doesn’t have too much involvement in the game.”

Okon also made a light-hearted joke, adding: “He plays on the left and will be close to me on the bench at some stage tomorrow, so I might have to trip him over as he’s running past.”

The former Socceroo captain said he expected his team to dominate possession as they did in the first two encounters against Perth.

With Roy O’Donovan’s suspension, Okon has opted to bring in Josh Bingham who has made just two appearances this season.

But the Mariners boss had faith the 22-year-old would make the most of his opportunity.

“We’re missing Roy which is a big loss, he scored eight important goals for us,” he conceded.

“Josh Bingham has an opportunity tomorrow and I think everyone who turns up tomorrow will be eager to see how Josh goes.

“We’ve been in every game this season. I don’t really have any concerns. When we have the ball, it’s those moments where at some stage we switch off and lose concentration where we’ve been punished. That’s a real focus for us.”

The Glory are coming off a 2-1 win over second-placed Melbourne Victory. 

Okon s said his side wanted to rectify last week’s 2-1 away loss to Melbourne City which saw his outnumbered team fight to the end.

“Perth on paper are a very strong team, they’ve had some good results,” Okon said.

“Last weekend’s game against Victory was a comeback win for them. I’m certain Kenny (Glory coach Kenny Lowe) is delighted with how they’re travelling.

“Every game has different challenges, for us we come into this game off the back of a disappointing episode there in Melbourne.”