England sacrificed opener Jason Roy to accommodate Brook, who has been marked out as a future superstar of the game because of his explosive batting.
Stokes, who reversed his shock one-day retirement to return to the squad, has not yet been ruled out of what would be a re-match of the 2019 final but skipper Jos Buttler revealed why England's number four batter was not fully fit.
"He's got a slight niggle with his hip. Fingers crossed that it will be good news for us," Buttler told reporters at the Narendra Modi Stadium on Wednesday.
"He's working hard with the physios and we'll know more when the guys arrive for training (later) today."
Test captain Stokes, who has long been nursing a troublesome knee, is back in the one-day setup purely as a batter and his record-breaking 182 against New Zealand last month proved what he is capable even in a reduced role.
England are naturally wary of rushing him so early in a six-week-long tournament.
"We'll make the right call here - if he's not fit to play, he's not fit to play," Buttler said.
"It's not the time to take big risk on someone at the start of the tournament."
Brook, an automatic pick in England's test side and part of their T20 World Cup winning team last year, is likely to be the beneficiary of circumstances.
"Harry, we all know, what a fantastic player he is. The start of his international career has been outstanding in T20 cricket and in the test format," Buttler said.
"He has not played loads of ODI cricket but it's a format that should suit him perfectly.
"It would allow him to bat for a long time and make big runs and that's something he enjoys doing.
"He's got all the shots. We know from test cricket, he can play big innings. So it's a format that should suit him really well."
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