The Wales No8 broke his collar bone in training, the Welsh Rugby Union said.
"The injury was sustained in an innocuous training ground incident and will require surgery," the WRU said in a statement.
Faletau (29) has 76 caps and his powerful running and destructive and consistent defence have made him an integral part of the Welsh pack since making his debut in 2011. He played in that year's World Cup and again in the 2015 edition.
He also played in all three tests for the British & Irish Lions in their drawn series in New Zealand in 2017 and won another Lions cap in Australia in 2013.
Wales face England home and away and also host Ireland later this month in their warm-up games for the World Cup in Japan.