"It's extra special,'' Medvedev said of facing Nadal for the first time. "I played Novak [Djokovic] and Roger [Federer] a few times. It's different. ... There is some extra pressure.''
Nadal won last year in Toronto for his fourth title in the event. He has 82 singles victories, and he won the French Open in June for his second title of the year.
Monfils, seeded 16th, outlasted 10th-seeded Roberto Bautista Agut of Spain 6-4, 3-6, 7-6 (2) in a match suspended Friday because of lightning. Monfils finally finished off Agut after a rain delay Saturday but battled a sore left ankle that forced him to withdraw from the semifinal.
"I love these matches, night session, Rafa," Monfils said. "I play tennis for that, for the big moments, big shows. It was [the] safest decision not to play."
Monfils consulted with his coach about the decision to withdraw.
"He said, 'You can't take the risk,'" Monfils said. "I had retired in Wimbledon. I came back. I played this week. I had played a huge match. It was risky to play another match because I could risk hurting myself for real."