Sri Lanka captain Sanath Jayasuriya is expected to be fit for Monday's crucial World Cup Super Six game against India at The Wanderers on Monday.
Jayasuriya suffered a bruised left forearm and a chipped bone in his left thumb when he was struck by Australia fast bowler Brett Lee in Sri Lanka's defeat to the world champions on Friday.
"I'd be surprised if he wasn't going to play. Personally I'm confident he'll be ready," Whatmore told Reuters after a net session on Saturday.
Should Jayasuriya not be fit, Sri Lanka have two contrasting left-handed batsmen who could play in his place, hard-hitting Avishka Gunawardene and the tall youngster Jehan Mubarak, who has played just four one-day internationals.
"Avishka is an opening batsman and the other guy (Mubarak) is more of a utility player, although he did open for us in a test match here and looked impressive. He's a good boy with potential," Whatmore added.
Sri Lanka's loss to Australia means they are now under pressure to win their last two Super Six matches to try and reach the semi-finals.
"It's an important match but I wouldn't say do or die. I'd be loath to call it that," Whatmore said. "I always try and get away from the result -- I'm a process-and-performance oriented coach, not results oriented.
"I think it weighs heavy on the shoulders if you are looking at the result. We work on the individuals and the things you have to do to get the result.
"I think there's a knowledge within the group that we're in a similar situation that we were in after Nairobi (after losing to Kenya in the first stage). We had two games to go to qualify for the Super Sixes and we're in the Super Sixes.
"Now we have two games to go to qualify for the semis. It's a test."
Saturday's net session was for squad members who did not play against the Australians, although batsman Mahela Jayawardene made an appearance.
Jayawardene made a three-ball duck against Australia and has managed just 16 runs in five innings at the World Cup.
"It was his personal choice," Whatmore said. "He had a long bat. We're hoping it was the right thing to do -- some people react better in the nets, others don't."