06/11/2013 06:57 EDT | Updated 08/11/2013 05:12 EDT

Central defender's injury does not seem major, but return date remains uncertain

VANCOUVER - The Vancouver Whitecaps will be without their top central defender Saturday when they host the New England Revolution.

Whitecaps coach Martin Rennie said Tuesday he does not expect Andy O'Brien to play. O'Brien suffered a hamstring injury in a weekend loss at Seattle, and remains out indefinitely. His absence leaves the Whitecaps with a shortage at central defender due to injuries.

Captain Jay DeMerit (ruptured Achilles) is out indefinitely while Brad Rusin (calf) is at least two weeks away from returning, and Carlyle Mitchell, recalled from lower-tier Edmonton, is recuperating from an ankle injury.

"It's just the timing," Rennie of the impact of the injuries. "It's unfortunate that they're all hurt at the same time. I've never really seen that. In recent times, there was one or two players in similar positions.

"But to lose four is tough. It's hard to deal with."

O'Brien's injury resulted two days after the Whitecaps traded versatile veteran Alain Rochat, who has experience playing central defender, to D.C. United for a pair of draft picks.

Rennie said an MRI showed that O'Brien's injury "doesn't seem too major," but there is no timeline for his return. Mitchell, who described himself as 75- to 80-per-cent fit, is the most likely candidate to replace O'Brien.

"His ankle seems to be getting stronger, so that's an encouraging thing for us," said Rennie. "Obviously, we've got a lot of players out at that particular position. So there could be an opportunity for him. Hopefully, he'll come through this week well, and he'll be ready to go."

Mitchell, a 25-year-old Trinidad and Tobago native who has represented his country internationally, played at total of five games for Vancouver in 2011 and 2012, but was loaned to Edmonton at the start of the season in order to get more playing time.

He expressed a willingness to play hurt, if necessary. The Whitecaps (4-5-4) sit seventh in the Western Conference while the Revolution, 5-4-5 before Wednesday's home game against New York, are also below the playoff bar in the East.

"It's a big challenge stepping in this weekend," Mitchell said. "But it's all about three points (for a win), and I'll do anything to get three points, so the injury doesn't matter now."

But the Whitecaps will be hard-pressed to replace O'Brien's experience, leadership and calm, steady play. He has quarterbacked the back line, barking out instructions to teammates to get in the proper position while playing every game this season and starting all but one.

Mitchell is expected to play alongside an unfamiliar partner in fellow central defender Johnny Leveron, a Honduran international who has recently established a place in the lineup as a result of Rusin's injuries. Rusin suffered a concussion before hurting his calf.

Rennie said Mitchell, whom Edmonton coach Colin Miller has described as his best player, can also be vocal if called upon. But, Rennie added, it will be necessary for players in all positions to communicate effectively without O'Brien directing the play.

The Whitecaps were leading the Sounders 2-1 in the second half before more than 53,000 fans at CenturyLink Field when O'Brien's injury turned the tables in favour of the home side. His replacement, Greg Klazura, committed a foul as a result of sloppy tackling in the Vancouver box, enabling Seattle to tie the game 2-2 on a penalty-kick.

And another defensive breakdown by Leveron and Klazura led to Seattle's winning goal from short range.

Vancouver striker Kenny Miller said O'Brien's injury spells a "huge loss," because he has been a "real presence" thanks to his experience and defensive qualities. Somebody will have to step up to fill the void, and Mitchell has a chance to claim a permanent position.

"It's about somebody coming in with a charge," said Miller.