Callaway dislocated his shoulder in a hurdles fall at Oamaru on Monday. He is having difficulty moving the shoulder, ruling out a medical clearance.
Hannam rode Cash Card to win at Oamaru on Monday for the Washdyke stable of Mel and Warwick Coles, who train Windwhistle.
Warwick has just spent a week in Timaru Hospital.
Hannam won the 2003 Winter Cup on Tuscany Warrior.
Windwhistle has also won over 1200m on a heavy (10) track at Riccarton and over the Winter Cup distance of 1600m. The track is rated a heavy (10) for tomorrow. He ran third to Comanche Gold and The Hammer Head over 1600m at Riccarton on June 23 at his last start.
"The horse is well. There could be a question mark about the track because the heavy tracks are all different," Mel Coles said.
Comanche Gold is a Riccarton specialist on rain-affected tracks. His five wins from nine starts on the track have been on slow to heavy surfaces. Four have been over 1600m, including a heavy (11) track.
He won a double in lower grades on slow track at the National meeting 12 months ago.
Superturf, winner of the race last year and Propel, the 2010 winner, are in the field tomorrow. No horse has won two Winter Cups since Rongonui won three in a row from 1988.
Propel is a 10yr-old. The only Winter Cup winner of that age was Mount Boa in 1933.
Propel won the Whyte Handicap (1600m) at Trentham at his last start. Superturf was fourth in that race.
Zennista and Innovation share favouritism at $5 in final field betting with the TAB, ahead of Superturf at $7.50.
Trainer Lisa Latta said Zennista was not suited by the track when the beaten favourite at her last start at New Plymouth on July 21.
Zennista is a 5yr-old mare, the age of Zabeel's Angel, the last mare to win the race, in 2001. Innovation is a 4yr-old and a mare of that age has not been successful since Kalott in 1967.
