Yes it is, although I'm not sure what contact has to do with anything.
Does Khedira have a history of hamstring issues, I really don't know? But muscular injuries are common in players returning from long spells out injured or inactive. Like I said before and what Allegri alluded to, it's a calculated risk pushing players in pre-season, because they have to be fit for the start of the season.
I understand that now he is injured it is a terrible signing and mercato disaster and all the rest, but we judge these things long term. If he ends up as the next Andrade it's a big flop, but players get injured. A bit too often in the Allegri era, for my liking.