Ruslan Ponomariov
There were plans for him to play a fourteen-game match against Kasparov in Yalta in September 2003, the winner of which would go on to play the winner of a match between Kramnik and Péter Lékó as part of the so-called "Prague Agreement" to reunify the World Chess Championship (from 1993 until 2006 there were two world chess championships). However, this was called off after Ponomariov refused to sign his contract without reservation.