Nishikori became the first Japanese man in the open era to reach the Melbourne quarter-finals thanks to his shock win over Jo-Wilfried Tsonga, but Britain's Andy Murray proved a step too far.
Speaking after his 6-3, 6-3, 6-1 defeat to the fourth seed on Rod Laver Arena, Nishikori, said he was delighted with the prospect of entering the top 20 when the next rankings list is released on January 30.
"That's exciting news for me because my first goal was to get top 20... it was a fantastic week for me. Now I'll try to get to the top 15," he said.
The 22-year-old also added that he was still a few years away from his maximum strength.
"Asians are different. Physically you have to get to 25 or 26 years old to build the body. It's different from other countries."