Elena Rybakina’s victory at the 2026 Australian Open has positioned her as the market’s lone realistic contender for a calendar Grand Slam, yet traders assign overwhelming probability to none achieving the feat across all four majors. The demanding transition between hard courts, clay at Roland Garros, grass at Wimbledon, and the hard-court swing at the US Open favors specialists and exposes even elite players to fatigue, injuries, and form dips over nine months. Historical precedent shows no woman has completed the sweep since the Open Era began, underscoring the physical and tactical barriers in a deep WTA field featuring consistent performers like Aryna Sabalenka and Iga Swiatek. Rybakina’s strong early-season record and serve-heavy style offer a narrow path if she maintains health and adapts across surfaces, though any slip at the French Open or Wimbledon would immediately reinforce the near-certainty of no calendar champion.