Miami Open: Naomi Osaka into last-16 by walkover as Nina Stojanovic withdraws
Second-ranked Osaka, the reigning US and Australian Open champion, will next face the winner of a later match between 16th seed Elise Mertens and 22nd-seeded Anett Kontaveit.
Miami: Japan's Naomi Osaka advanced into the fourth round of the WTA and ATP Miami Open by walkover on Sunday after Serbian Nina Stojanovic withdrew due to a right thigh injury.
Second-ranked Osaka, the reigning US and Australian Open champion, will next face the winner of a later match between Belgian 16th seed Elise Mertens and 22nd-seeded Anett Kontaveit of Estonia.
"I'm sorry I can't continue my participation at the Miami Open due to my recent injury during my singles match," 95th-ranked qualifier Stojanovic said in a statement.
Osaka, who lifted her fourth Grand Slam title last month in Melbourne, is seeded second behind top-ranked Australian Ashleigh Barty.
Monfils, the runner-up in Monte Carlo to Rafael Nadal in 2016, was scheduled to face Pablo Andujar in the first round.
Monte Carlo Masters: Stefanos Tsitsipas beats Dan Evans in straight sets to set up final against Andrey Rublev
Fourth seed Tsitsipas needed just over an hour to dispatch Britain's Evans, who knocked out world number one Novak Djokovic in the last 16.
Both world No 136 Nagal and world No 124 Kovalik came into the main draw through qualifying rounds and the Slovak prevailed 3-6, 6-1, 6-3 in a contest that lasted for two hours and 13 minutes.