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 face Ross County in the Clydesdale Bank Premier League at Dingwall on Saturday, 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.
"Eventually I went on the pitch to make sure he was coming round.
"I knew he was in the best possible hands but from my point of view I just wanted to make sure he was okay.
"He had a fantastic game and he just didn't deserve that.
"Thankfully he was able to come home with us and get the best treatment."
Lennon also had injury concerns over Scott Brown (hip), James Forrest (groin), Anthony Stokes (ankle), Gary Hooper (hamstring) and Paddy McCourt (groin) but they could all be available for the Dingwall clash.
