The midfielder was stretchered off with an ankle injury just before half-time in Saturday's 1-1 friendly draw at Tranmere and early indications suggest he will not return to the fold until September.
Manager Paul Simpson, who is already trying to utilise a small squad, told the club's official website: "It is a bit of a blow to have lost Lewis for the start of the season but sometimes injuries such as these can take a lot longer to recover.
"Lewis has shown some good signs in the pre-season campaign and he is really disappointed that he will be missing.
"It gives us a little headache for the next few games but there are options in the squad that can come in to cover."
Meanwhile, Shrews have been handed a bye into the second round of this season's Johnstone's Paint Trophy, one of 16 clubs who will not compete in the opening stage.