The Irishman, who spent last season on loan at Ipswich, limped off in the first half of Celtic’s 2-0 friendly defeat by Real Madrid on Saturday night.
Manager Neil Lennon told Celtic TV: “It is a grade one hamstring and it looks like it’s going to be three or four weeks.”
Murphy’s injury was overshadowed by a later and more concerning blow to 19-year-old Dylan McGeouch, who broke his jaw and was knocked unconscious in an aerial challenge with Nuri Sahin.
Lennon said: “He has had a plate inserted so it should be four or five weeks.”
The Celtic manager, whose team travel to Ross County in the Premier League tomorrow, admitted he was deeply concerned as McGeouch lay motionless on the pitch in Philadelphia.
“That’s one of your players there and your first instinct is almost like a fatherly one,” Lennon said. “You just hope he is going to be okay.”