Robert Deutsch-USA TODAY Sports

It's been more than two weeks since Serena Williams was seen on a tennis court when her quest for the calendar-year Grand Slam came to an end at the U.S. Open semifinals, and if her coach has his way, it will be a long time before she's playing again.

Speaking to Melissa Isaacson of espnW.com, Patrick Mouratoglou said Williams' focus on the majors may have left her mentally drained for any of the remaining events this season:

When she lost in Toronto [in August], she was very disappointed, but we went back to practice the morning after because she wanted to win the US Open. But after this year and the three Grand Slams [she won in 2015], the question is how high her motivation is to play those tournaments. I don't think she should play if the motivation is not really high.

Isaacson did mention Williams is slated to play in two more events this season, the China Open and WTA Finals in Singapore, both in October. The world's top-ranked player did win the WTA Finals last year, defeating Simona Halep.

Mouratoglou emphasized that he wasn't questioning Williams' motivation for upcoming years—just that everything she went through physically and mentally while trying to capture the four major titles in 2015 would make any other event still on the schedule feel like a letdown.

"I have no doubt the motivation will be there and no doubt she'll be the same Serena," Mouratoglou said. "She just won four Grand Slams in a row and got to the semifinals of a fifth. It's not time to doubt whether age will affect her. She has a lot of time left."

The veteran coach said he thought Williams "was not in the right mindset" against Roberta Vinci because she had defeated the Italian star handily in their four previous matches, though also acknowledged in the past he has found "a way to make her be better on those days."

There is something to be said for taking a mental break. The 34-year-old has had inconsistencies in the past when it looked like her motivation level wasn't very high or she wanted to be doing something else because no one can challenge her at her best.

When Williams is motivated and poised to make a statement to anyone who doubts her, she has seasons like she did in 2015 with five singles titles, three majors and a 53-3 record.

Ultimately, the decision to play more events in 2015 is Williams'. She doesn't have to win another tournament this year to validate anything, but it would be nice to have her back to end the season on a high note heading into next year.