Salah was forced off in the first half of Saturday's Champions League final after a nasty clash with Real Madrid's Sergio Ramos.
The forward was in clear discomfort after injuring his shoulder, and was powerless to stop Madrid taking a third straight title with a 3-1 win in Kiev.
His presence for the Pharaohs in the World Cup is now in serious doubt, with Saudi Arabia Sport Authority chairman Turki Al-Sheikh affirming he would miss out.
According to Salah's friend Aly Mazhar, however, he will be back in time to line up for the nation in their first finals appearance since 1990.
"Three weeks inshalla! It’s a strain and he’ll be back on the field in three weeks," Mazhar claimed in a Facebook post on Sunday.
The 25-year-old has picked up 57 caps for Egypt to date, scoring 33 goals.
He also netted six in the third round of Africa's World Cup qualifying campaign to take his country to Russia ahead of Ghana, Uganda and Congo, a feat that earned him the African Footballer of the Year award.