Przysiezny, No. 112 in the world and looking for his first ATP finals appearance, was up 6-3, 5-3 when Fognini said he couldn't continue. Przysiezny had dropped just eight points over nine games serving and hadn't seen a break point in building his lead.
He'll go against seventh-seeded Lukas Rosol in the quarterfinals. Rosol was a 6-4, 6-4 winner over Karen Khachanov as he had five breaks in 10 receiving games.
No. 4-seeded Dmitry Tursunov took out Konstantin Kravchuk 6-3, 6-0, losing one point on serve and seven overall in second set. His next opponent is Joao Souza, who outlasted Sergiy Stakhovsky 3-6, 6-4, 6-0.
Sixth-seeded Ernests Gulbis defeated Jurgen Zopp 6-3, 1-6, 6-3 and draws Roberto Bautista Agut in the quarterfinals. He capped second-proud play with a 2-6, 6-1, 7-6 (7-5) win over Evgeny Donskoy.