Tennis: Improved fitness can spark Nishikori glory

London - Japan's Kei Nishikori admits his number one goal in 2016 is to stay healthy enough to make a sustained push for Grand Slam glory.

Nishikori has endured a frustrating campaign over the last 11 months with a series of nagging injuries ruining his hopes of challenging for the four majors.

After making his Grand Slam breakthrough with a run to the final of the 2014 US Open, the 25-year-old came into this year tipped as the most likely challenger to the sport's big four of Novak Djokovic, Roger Federer, Andy Murray and Rafael Nadal.

But instead he was beaten in the quarter-finals of the Australian and French Opens and then pulled out of the Wimbledon second round due to a calf injury before suffering an embarrassing US Open first round defeat.

Nishikori remains certain he has the required talent and stamina to take home silverware from the Grand Slams and the Masters 1000 tournaments, but to do that he knows he must steer clear of those troublesome calf and hip complaints.

"I'm excited for next year. I think physically I have to be little more strong," Nishikori said after his season came to an end with a defeat against Federer at the ATP Tour Finals in London on Thursday.

"I try to work on little things to improve a little more. Try to be healthy, I think that's most important." It wasn't all doom and gloom for Nishikori in 2015 as he did win three titles - in Memphis, Barcelona and Washington - as well as maintaining his place in the world's top eight.

For the second successive year, Nishikori qualified for the prestigious Tour Finals at the O2 Arena and he took heart from the way he recovered from an opening-match thrashing at the hands of world number one Djokovic.

A less competitive player might have thrown in the towel after winning just two games against Djokovic.

However, Nishikori's ferocious will to win is one of his main assets and he recovered to defeat Tomas Berdych in his second group match.

Chasing a third career win over boyhood idol Federer, Nishikori broke the Swiss great five times and pushed him to the limits before succumbing to a 7-4, 4-6, 6-4 loss that confirmed his elimination.

Those strong performances have given Nishikori renewed hope of a strong 2016 and he said: "I think for me it's important to win a title, especially big ones, Masters, going further in a Grand Slam especially, because I didn't do quite well this year.

"Plus I missed three Masters this year, but still I'm in the top 10.

"If I can do little better than this year, I think I can go little higher (in the rankings).

"I think I have to adjust little things to win those top players. But I think getting close." One of Nishikori's main aims during his three-week training camp ahead of January's Australian Open is to improve his play at the net.

"I'm trying to work on coming into the net a little more. I am improving a lot this year. I want to keep doing that," he added.

"It's going to be really important, making a lot of first serves. I'm not the guy acing a lot, so I have to raise the percentage little more."