Defoe limped out of last weekend's game against Real Salt Lake with a hamstring injury and no date for a return has been set.
The England striker has adapted to life in MLS remarkably well and has netted three times already this season. However, Defoe has struggled with injuries during the latter part of his career and will hope to make a speedy return to action.
The former Tottenham Hotspur man made the move to Canada earlier this year on a four-year deal. Defoe has said that he still retains hopes of making the England World Cup squad this summer but this setback combined with the current form of Daniel Sturridge, Rickie Lambert and Jay Rodriguez could end those dreams.
Defoe last England call-up came in early March in the 1-0 friendly win over Denmark, although the striker did not feature in the match.
Toronto FC travel to Columbus on Saturday before facing Colorado the following weekend. It is unclear at the moment if Defoe will be available for that game.