Veteran centre backs Steven Caldwell and Damien Perquis, who did not play in Sunday's 2-1 loss at Real Salt Lake, are both questionable for Saturday's game in Chicago.
The two centre backs are dealing with calf problems and coach Greg Vanney says both are questionable this weekend.
Vanney had hoped Perquis would be ready for Salt Lake. But the team eventually decided not to risk the Polish international, keeping him on the bench.
With a bye after the Chicago game, there is added incentive not to push the two defenders back into action too quickly.
The weekend loss dropped Toronto's MLS record to 1-2-0.
"We could have played better," said Vanney. "There were things in that match that I thought we could have taken advantage of and we didn't."
In addition to its two injured centre backs, Toronto was without starting fullback Justin Morrow (suspended) and star midfielder Michael Bradley and striker Jozy Altidore (U.S. international duty).
All three are expected back for Chicago (1-3-0).
On the plus side, the makeshift backline of Ashtone Morgan, Clement Simonin, Nick Hagglund and Warren Creavalle fared quite well, considering.
"On the defending side I thought by and large we were OK," said Vanney. "Clearly dealing with crosses is something we've got to get better at."
Both Salt Lake goals came off Javier Morales crosses, defensive letdowns in which the back four got little help from the Toronto midfield in tracking late runs.
It's been a longtime weakness for the club.
Vanney says his team could have cleaned up the mess long before the ball got to the penalty box on the Salt Lake goals.
"It's almost like a comedy of errors, if you will, that we need to take care of and then the ball doesn't end up in the box," he said.
On the winning 89th-minute goal by Jordan Allen, Vanney counted three chances at nipping the play in the bud.
Adding to his frustration was that the goal came one minute after Toronto had tied it up.
"When you get yourself back in the game, we shouldn't have been celebrating at that moment. We should be celebrating five minutes later when we finish the game and we end it 1-1. ... We needed more concentration, more conviction from the group to make sure that they got nothing in the final three minutes."
Conceding late goals has also been a franchise Achilles heel at times.
Toronto's lone goal, by Brazilian substitute Jackson, was a thing of beauty. Starting with goalie Joe Bendik, the goal was the product of 12 passes and went through 10 Toronto players.
Italian playmaker Sebastian Giovinco, meanwhile, looked more dangerous as the game wore on.
Complaining about refereeing has also been a recent constant, with Morrow's sending off in Columbus and a Nick Hagglund goal in Salt Lake called back for holding.
Vanney opted for humour when asked if there was protocol for dealing with such controversy.
"The first step is I go irate," he said dryly. "The second step is I scratch my head and try to figure out what's happening. And then calm prevails and we actually try to find out what exactly was seen and what the call was. To my knowledge there hasn't really been a response yet. It is what it is at this point."
"We're better than they are. We should have won the game."
Vanney said defenders Eriq Zavaleta (ankle) and Mark Bloom (quad) were "borderline questionable-probable" for Chicago.
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