Japan's Kei Nishikori will miss the National Bank Open in Canada, an ATP Masters 1000 event, due to a left knee injury, the tournament organizers said Friday.
The 33-year-old has withdrawn from two tour events in a row after he also skipped the ongoing ATP 500 Mubadala Citi DC Open with the same setback.
The former world No. 4 had hip surgery in January 2022 and won his comeback tournament in June at the Caribbean Open, an ATP Challenger Tour event in Puerto Rico.
He returned to the ATP Tour last week for the first time since October 2021, losing in the quarterfinals at the ATP 250 Atlanta Open.
Nishikori has been named on the men's singles entry list for the U.S. Open starting Aug. 28 in New York, where he played his last Grand Slam in 2021.