Toronto FC captain Torsten Frings will be out for four to six weeks with a strained right hamstring.
The former German international was injured during Toronto's season-opening 3-1 loss in Seattle on Saturday.
Playing in central defence, Frings was hurt in the 23rd minute as Fredy Montero sent a long ball to David Estrada from within the Seattle half.
The 35-year-old Frings cut out the ball, poking it skillfully out of play with his right leg in the penalty box. But both players went down and Frings was slow to get up.
When the Toronto FC trainer got there, Frings got up and limped off the pitch.
Frings, a defender-midfielder, is arguably Toronto's most influential player.