Stan Wawrinka has revealed that he is eager to get back to his best and start challenging for the major titles but is aware that it is difficult to reach the top after returning from a long-term injury absence.

The Swiss number two missed the second-half of last season due to a knee injury that required surgery. Wawrinka ended his 2017 season after his first round loss at Wimbledon and only returned to action at the Australian Open this year.

The 32-year-old lost in the second round in Melbourne but revealed that it was necessary for him to play to understand if his knee can sustain the pressure of playing competitive tennis. Wawrinka is now playing his second tournament of 2018 at the Sofia Open and is hoping to continue his path to full fitness.

"I am feeling much better," Wawrinka told the Sofia Open's official site. "Since the first day I came back from Australia, I was working really hard physically and also for my tennis. I am feeling better and better and starting to come back to my top level."

"For me, it was really important mentally, but as well - for my knee to see that everything is going in the right direction. I knew I wasn't ready to play in a good level and physically I was still far away from I want to be.

"But it was important to test the knee, to see how it is reacting and also mentally to be a little bit back in the tour," he added.

Wawrinka is one of the few players who threatened the stranglehold of Roger Federer, Rafael Nadal and Novak Djokovic in the last decade. The trio have won 33 of the last 41 Grand Slams with the other eight being shared by Wawrinka and Andy Murray – three titles each - with Marin Cilic and Juan Martin del Potro winning one apiece.

Wawrinka was ranked world number three before being struck by the injury in 2017 and he is keen to get back to that level and start challenging for the major titles - he is currently ranked number 15. But Wawrinka is aware that coming back to his best will take time owing to the severity of his injury.

However, veterans Nadal and Federer have proved that it is possible after they returned from long-term absence to get back to the top of the world rankings. The last five Grand Slams have been won by the duo - three for the Swiss ace and two by the Spaniard.

"My main goal is to come back at my top level physically and tennis-wise. I know it was really tough to be out for six months.

"Big surgeries take time to come back. So that is my first goal. When I feel ready for everything then I will try to see what more I can achieve," the three-time Grand Slam champion explained.