The Canadian international suffered a tibia and fibula fracture in a match with his club BSC Young Boys on Wednesday.
According to the BSC Young Boys website, Simpson fractured a tibia and fibula following a tackle in a game against FC Basel in the Swiss Super League finale. The 29-year-old underwent surgery in the hours following the injury, which took place just before halftime of the match.
The injury is a big blow for the Canadian national team, as Simpson, who was named to Stephen Hart's 23-man roster for a national team training camp that started this week, will miss Canada's next round of World Cup qualifying matches next month.
Simpson has earned 43 caps and four goals for Canada.