Pietersen is currently on the sidelines with a troublesome knee injury that will also keep him out of next month's Champions Trophy, but England are confident the batsman will be back in time for the Ashes. That means one of the current incumbents - probably Jonny Bairstow but possibly Nick Compton - would have to give way.
"I think we all know when hopefully Kevin comes back and he's fit, his record and his class pretty much demands that he plays for England," said Cook. "His record allows him to do that. So of course that creates competition for places, and the guys in the changing room will be desperate to score runs."
He added: "That's good for us in this game because we need as many runs as we can. If any batter scores runs it's very hard to leave him out. That's how selection works. I don't think it will give them any extra motivation because I don't think you need any extra motivation when you're playing for England...but we all know that's the situation."
Cook was also able to offer a brief update on Pietersen's rehabilitation, adding: "Kevin's progressing well from his injury. There is obviously some more information coming over the next couple of weeks but chatting to him last week at Lord's he sounded positive, and it's fingers crossed.
"With injuries you're not quite sure how they're healing but it sounded as if he was making good progress."
England go into the match 1-0 up in a two-game series and looking for another victory to weigh against three draws in the reverse series earlier this year.
However, Cook is not expecting a bowler-friendly wicket and believes it will be key for England to cash in when the conditions are in their favour and battle when are not.
He said: "Over the last couple of years I think the pitch has got better here and it's produced some high-scoring games. This year in the county championship there's been some high-scoring games here too.
"It's pretty similar to Lord's where it's more to do with the overhead conditions. If it's sunny it can be really nice to bat and if it's cloudy it can be tough to bat. You've got to fight through those sessions when they arrive."