Pietersen was unable to take the field for the final two days as England opened up a 2-0 lead over Australia at the home of cricket and will face intensive treatment in a bid to get him back on the pitch for the Old Trafford Test, which begins on August 1.
Pietersen has already missed three of England's seven Test this year with a knee problem and was ruled out after two games of the 2009 Ashes, but remains an automatic selection when available.
Captain Alastair Cook admitted there was ongoing uncertainty over his fitness and almost talked himself into making it an even bigger concern before correcting himself.
"Clearly it's a concern. He's got a tear...sorry, a slight strain of his calf," said Cook.
"Sorry, that was a bad slip of the tongue - it is a strain. But it is a concern.
"We've got a great medical team who will work non-stop over the next week or so to try and get him fit for Old Trafford."
England do not have an obvious candidate to replace Pietersen and would probably have to choose from a group of players they are not entirely convinced by for a variety of reasons.
Eoin Morgan, James Taylor and Ravi Bopara are among those to have tried and failed to nail down a place, recently dropped opener Nick Compton is almost the direct opposite of a like-for-like replacement and Gary Ballance is well thought of but uncapped.
"Kevin is a world-class player with 22 Test hundreds...clearly that leaves a big hole if he's not there but if he's not available it gives someone else the opportunity to step up," said Cook.
"There are a lot of good players not playing in this team."
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