The left-armer suffered a shoulder problem while playing for Mumbai Indians in the Indian Premier League.
He will definitely miss India’s opening match against Bangladesh on 6 June, but captain Mahendra Dhoni says the overall prognosis is positive.
“Zaheer is most likely to get fit by the second or third game,” he said.
The 30-year-old played six matches for Mumbai in South Africa, picking up six wickets before injuring his left shoulder.
He is one of five seamers selected by India for the World Twenty20 and Dhoni believes the rest also have the ability to utilise the conditions in England.
“We have a lot of bowling options,” said Dhoni. “We have got talent like Praveen Kumar, RP Singh who can really swing the ball, and Irfan Pathan.
“Our part-time bowlers, especially spinners, have done well in the IPL. We bat right down to number eight or nine. We have a very balanced side. We need to focus on playing to our potential and hopefully we can defend the title.”
India are the bookmakers’ favourites to win the tournament which culminates in a final at Lord’s on 21 June.
Former Australia captain and India coach Greg Chappell said Dhoni’s team were strong contenders to retain their title.
“India has slight edge over other teams, with trump cards like Dhoni and [batsman] Yuvraj Singh,” said Chappell.
“Dhoni is among the best captains today. Yuvraj was out of colour in the IPL but is one of the most dangerous batsmen in the shortest form of cricket and will give headaches to rival captains.
“Indian players are very well prepared after the IPL.”
India squad: Mahendra Dhoni (capt & wk), Virender Sehwag, Gautam Gambhir, Suresh Raina, Yuvraj Singh, Yusuf Pathan, Rohit Sharma, Harbhajan Singh, Zaheer Khan, Ishant Sharma, Praveen Kumar, RP Singh, Ravindra Jadeja, Pragyan Ojha, Irfan Pathan.
