Fast bowler Hasan Ali believes the fever which has spread through the Pakistan team at the World Cup has been caused by being largely confined to their hotel.
"We can't go out much. If we do want to go out, we have to go with an entire security team," said Hasan on Thursday.
Pakistan are on their first visit to India in seven years while only two of the 15-man squad had ever played in the country before this World Cup.
The tense political and diplomatic relationship between the two neighbours means that Pakistan and India meet only in international cricket tournaments, not bilateral events.
Pakistan's participation in the World Cup had hinged on security clearance from Islamabad and even when it was given, the government said it still had serious reservations over security for the team.
Visas for the Pakistan squad were only issued two days before their departure.
"The hospitality is good and we are taken good care of, but we cannot go outside and we have to tell the security before going out because security is an issue," added 29-year-old Hasan, who has an Indian wife.
Asked about the 13 fit players available for Friday's game against Australia, Hasan replied: "Yes, most of the players have recovered from fever but when you live in a hotel room then room sickness happens."
Six Pakistan players -- Abdullah Shafique, Shaheen Shah Afridi, Mohammad Rizwan, Agha Salman as well as reserves Mohammad Haris and Zaman Khan were laid low with flu and fever on Tuesday.
Pakistan supporters from across the border have been effectively banned from the World Cup after a failure to gain visas.
Only a handful attended the high-profile clash with India at Ahmedabad's 132,000-seater stadium, mostly expatriates from the United States and United Kingdom.
"The number of fans has increased and with journalists they are now about 45-47. Yes, we are missing our fans but that is not in our hands," said Hasan, who is Pakistan's leading wicket-taker at this World Cup with seven.
The Pakistan team faced a hostile crowd in Ahmedabad, prompting the Pakistan Cricket Board (PCB) to lodge a complaint with the International Cricket Council.
They protested over the "inappropriate behaviour" of Indian fans towards the Pakistan players.
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