Baseline Buzz: Mixed expectations for Serena, Murray this fall

— -- The US Open might be over, but that doesn't mean this year's tennis season has ended. Sure, the fall circuit doesn't garner as much attention, but there is still a lot on the line. Here are some of the remaining pressing questions as they relate to the top-tier stars' immediate future:

Which top-5 men's player is most in need of a strong fall season?

Nic Atkin: It's tempting to say Andy Murray after the way his summer fizzled out, but Rafael Nadal is the man from the top 5 with most work to do. He was unconvincing in New York and is still clearly working his way back to full fitness after his wrist injury. But more people than ever will be doubting that he can add a 15th major title before he hangs it up. Qualifying for the ATP World Tour Finals is a must if Rafa wants to prove he can once again be a threat at the Grand Slams.

Peter Bodo: The obvious answer is Novak Djokovic, but my choice is Murray because tennis sorely needs a challenger to the Serb in 2017. Murray seemed to hit a wall at the US Open exactly when Djokovic seemed vulnerable. Rebuilding Murray's momentum and credibility as a threat at a time when Roger Federer is a question mark and Rafael Nadal continues to struggle mentally would provide a great storyline for the new year.

Greg Garber: While Djokovic could use a few positive results, I think there's more pressure on Nadal. After losing the bronze-medal match at Rio to Kei Nishikori, Nadal went out in the fourth round of the US Open, courtesy of Lucas Pouille. Rafa, a momentum player, needs to put down a few successes to set himself up for 2017.

Johnette Howard: Nadal's unavailability for Davis Cup under confusing circumstances -- some team members said his wrist was the issue; others said he merely had the flu -- raises questions about whether he'll ever be a Grand Slam winner again. It's been a long time.

Melissa Isaacson: After losing to Pouille in a fourth-round, fifth-set tiebreaker at the US Open, it would be easy to call it just another disappointing finish in a major for Nadal. But after dropping out of the French Open and Wimbledon with a wrist injury, it was a sign of progress for Nadal, who said his body is ready to be pushed again. A tournament win or two at this point is essential to further that progress.

Which top-5 women's player is most in need of a strong fall season?

Nic Atkin: Since beating Serena Williams in the French Open and appearing to signal she was one of the new faces of women's tennis, Garbine Muguruza has fallen early at both Wimbledon and Flushing Meadows. Angelique Kerber has firmly taken on that mantle as the game's new star, but Muguruza can remind everyone why she was in the conversation in the first place with a strong finish to the season.

Peter Bodo: Muguruza did a good job at the tail end of last year recapturing the form that enabled her to reach the 2015 Wimbledon final. She won her first major at the French Open in 2016, but once again failed to back it up, so another strong fall would position her as a strong contender for a No. 1 ranking that seems to be up for grabs in 2017.

Greg Garber: Since winning the French Open, Muguruza is a less-than-stellar 7-5. She lost in the second round of the US Open and must find a way to pull it together.

Johnette Howard: Muguruza has taken a step backward rather than a leap forward since her terrific performance to beat Williams in the French Open final. The swagger she voiced later has evaporated. Talented, but an enigma.

Melissa Isaacson: After second-round exits at Wimbledon and the US Open, Muguruza desperately needs to rediscover whatever it was that led her to the French Open title. More important than rankings implications is the longer she stays in a funk, the more likely she won't be able to snap out of it.

Which top-5 men's player should seriously consider taking extended time off?

Nic Atkin: It's probably a no-brainer that Andy Murray needs an extended rest. He pushed his body to the breaking point over a grueling summer, and it all finally caught up to him physically and mentally when he melted down in the US Open quarterfinal against Nishikori. Then, at the Davis Cup, Murray played (and lost) the longest match of his life, against Juan Martin del Potro. Great Britain ultimately lost the Davis Cup tie. Murray should stick with the ice baths for a month or so to preserve his chances of winning more majors.

Peter Bodo: Tennis was abuzz with the prospect of a calendar-year Grand Slam by Djokovic as Wimbledon began last year, then he was derailed through the US Open by a combination of erratic form, personal problems and injuries. Djokovic is 29 now, and it might be a wise idea for him to take a significant break, exhibitions included, to prepare for another push that could net him more Grand Slams -- or the major singles title record held by Roger Federer (who has 17 to Djokovic's 12).

Greg Garber: Murray had to be exhausted after winning gold in Rio, then reaching the final of Cincinnati a week later. He lost in the US Open quarters, then played the Davis Cup semifinal, where he lost to del Potro in the opening rubber. Time for a refreshing nap, then a run at the year-end title at home in London.

Johnette Howard: I guess this is my pile-on Nadal week. While he needs extended time off, he needs positive results as well. He can have both. It felt like he rushed back for the Olympics and US Open, and the results weren't good. He should take a lesson from Federer and del Potro's injury struggles and rest for a little while and recover. Then finish the season strong, hopefully at the year-end championships.

Melissa Isaacson: After reaching his third Grand Slam final of the year and having won two, Djokovic hardly seems desperate for a strong fall season. But since his French Open title in May, Djokovic has not been himself. He needs to shake off the doldrums and whatever else is ailing him. An end-of-year break might do him a world of good.

Which top-5 women's player should seriously consider taking extended time off?

Nic Atkin: Serena Williams refused to blame fitness as the reason for her stunning US Open semifinal loss to? Karolina Pliskova. But the fact is Williams is now 35. It was once unthinkable, but her time at the top might be up, with younger, hungrier competitors snapping at her heels. Missing the fall schedule, as she did last year, will give Williams as good a shot at possible of breaking Steffi Graf's major title record, at the Australian Open.

Peter Bodo: Simona Halep is clearly spinning her wheels at No. 5, and she simply hasn't conquered her "big-matchitis." Perhaps it's time for the Romanian dynamo, who has the counter-punching game and fabulous wheels to outgun and outrun anyone, to take a break and reassess her attitude and expectations.

Greg Garber: I'm going to say No. 1 Angelique Kerber. While Williams, who turns 35 next week, could use a rest, Kerber should shut it down for a few weeks after reaching the finals in Rio and Cincinnati and winning the US Open.

Johnette Howard: Serena. Like a lot of top players in this Olympic year, she was hurt and playing on fumes by the end of the US Open. Williams has nothing to prove and enough money banked to skip the WTA's year-ending event in Singapore, and say see you next year. Majors are all she needs to chase at this point.

Melissa Isaacson: Taking time off has rarely been a negative for Williams, and as she gets older, taking well-timed breaks is even more important. With a sore knee contributing to her semifinal loss to Pliskova at the US Open, skipping the end-of-year tournaments as she did last year may be just what she needs.