As the tennis tours warm up for the U.S. Open in the summer heat of North America, the sport’s most accomplished players will arrive in New York cold.

The five active players with the most Grand Slam singles titles to their names — Serena Williams, Roger Federer, Rafael Nadal, Novak Djokovic and Venus Williams — are missing from both this week’s National Bank Open in Toronto and Montreal, and next week’s Western & Southern Open in the Cincinnati suburbs. The veterans have all played selective schedules this year, but their wholesale absence from the warm-up to the year’s final major tournament, which begins on Aug. 30, is striking.