The Reds will be without a number of regulars because of international duty, injury and suspension when they host the Portland Timbers in Major League Soccer action on Wednesday night.
With the absences, though, brings a chance for some of Toronto's fringe players to step up in front of the home crowd at BMO Field.
"It's the same old story. Everybody wants to play so now people are going to get the chance to play," Mariner said. "We've got experienced players in there so it should be a tremendous ding dong battle."
Despite Mariner's faith, TFC's defence has been hit especially hard. The newly-signed Darren O'Dea is with the Republic of Ireland for a friendly against Serbia, while Dicoy Williams (Jamaica) and Doneil Henry (Canada) are also on international duty.
Logan Emory was expected to be back from his suspension for Wednesday, but because Toronto agreed to postpone last Saturday's game in Columbus so that the Crew could attend the funeral of teammate Kirk Urso, the defender will miss out against Portland.
Add the injury problems facing Jeremy Hall and Mariner has few options for a makeshift backline that will likely include Adrian Cann and Ty Harden.
"I just want them to relax and do the job," Mariner said. "I think that in the system, if everybody is doing their jobs to the best of their ability then we'll be OK because we're in it together.
"We're doing one-and-a-half jobs on the field when we're out of possession. That's the way you've got to think about it — you've got to go the extra mile for your mate."
Cann, who hasn't seen action in MLS play since June 16 because of a knee injury, looks set to start in the centre of defence alongside Richard Eckersley. Ashtone Morgan practised with the first team at leftback on Tuesday, while the out-of-favour Harden could see his first league action since April 7 on the right.
"I'm a competitor. I'm always up for playing in matches and getting stuck in so I'm excited," Cann said. "It'll be a good match. Guys that usually don't get to play a lot get an opportunity to show the coach what they have."
Added Eckersley: "(Cann and Harden) aren't new to the team. I've played with them before. It's just a case of getting through the first ten minutes or so. Then I think everything will slot into place."
Toronto goalkeeper Milos Kocic sees Wednesday's game as an opportunity for some of his teammates to show the coaching staff they belong in the regular starting 11.
"I think everybody deserves a chance," he said. "I don't think it's going to be a problem. I think we need to be focused first, get a couple of touches on the ball, get confidence and then as the game develops make sure we don't give up silly goals."
But the defence isn't the only area of concern for Mariner. Also missing out for the Reds because of international callups are midfielder Terry Dunfield (Canada) and forward Ryan Johnson (Jamaica).
"I always want our players to play for their national teams," Mariner said. "Terry loves his country with an unbelievable passion and I think it's important that he plays for his country because how many more caps is he going to get at his age?"
Aaron Maund was in the heart of the midfield at practice and could get the first start of his MLS career alongside Eric Avila, Reggie Lambe and captain Torsten Frings, with Eric Hassli and Luis Silva paired up front.
Toronto FC (5-13-4, 19 points) sits last in the MLS standings and can overtake Portland (5-12-5, 20 points) with a win, but Kocic is wary of striker Chris Boyd, who has seven goals in MLS play this season.
"He can strike from everywhere so I have to be very careful and obviously the defenders have to be very smart how they deal with him," Kocic said. "It's going to be a handful for the defenders, but I trust my defenders and I think we're going to do a good job."
Notes: Mariner said striker Danny Koevermans underwent surgery to repair his injured left knee in Toronto on Tuesday. The Dutchman tore his anterior cruciate ligament against New England last month and isn't expected back on the field until next May. ... Mariner also said that midfielder Matt Stinson has a thigh injury and will be out a month.