Goalkeeper Glen Moss, who was outstanding during last Sunday's 0-all draw with Melbourne City, has come through the week well after suffering a cork in his leg against City. Midfielder Vince Lia (hamstring) is also likely to be available for selection tomorrow.
"It's the right time of year for all the injuries to come good," Merrick said. "But there's good competition out there and there's a good atmosphere in the camp."
Before last week's stalemate with City, the Phoenix dropped back-to-back home games via a 3-0 margin to Sydney FC and the Victory, which all but took them out of contention for the Premiers Plate.
Given Perth are likely to be out of the playoffs due to their reported salary cap breaches, the Phoenix will finish inside the top four but a top-two finish would give them greater advantages in the post-season.
The Mariners are out of the playoff race but represent a tricky challenge as they continue to bed in under new coach Tony Walmsley.
"There's always that honeymoon period," Merrick said. "So they'll play with no real responsibilities and some of them will play to make sure they're signed for the following season. But they'll be an attacking outfit and I think it'll be a good preparation for us going in to the finals."
