(REUTERS) - John McEnroe says the ATP Tour must consider reviewing its schedule in a bid to cut down on injuries after Canadian Milos Raonic joined the list of top players sitting out the US Open.

While Raonic (wrist) is expected to rejoin the Tour later in the year, the three other high-profile absentees from Flushing Meadows - Novak Djokovic (elbow), Kei Nishikori (wrist) and Stan Wawrinka (knee) - have been ruled out for the rest of the season.

Seven-time Grand Slam winner McEnroe said players had become more prone to injuries as the game evolved over the years, and said officials should take another look at the schedule to see if they can lighten the load.

"They have worked over the years to get it down to nine or 10 months," McEnroe told ESPN.

"I think perhaps they would be better served to continue to look at that.

"Sometimes it's unpredictable. But certainly the wear and tear is there, because the ball is being hit harder so you have to react quicker. So things happen more often than they did in the past. That's part of why you're seeing a lot of injuries.

"But let's face it, there have been injuries for a long time. This is nothing new. They are going to continue to look at it... we should continue to try to figure out ways to get the maximum out of all the players."

Swiss ace Roger Federer and world No. 1 Rafa Nadal were sidelined for the latter stages of last season as they sought to recover from long-term injuries.

Federer withdrew from the Cincinnati Masters earlier this month due to a back injury while world No. 2 Andy Murray has struggled with a hip problem since the French Open, but both have said that they would play in New York.

The US Open, the final Grand Slam of the season, is being held from Aug 28 to Sept 10.