Frankel has been ranked as the world's best horse for at least the last 25 years by British Horseracing Authority handicapper Dominic Gardiner-Hill.
Victory in Saturday's JLT Lockinge Stakes at Newbury saw Frankel's rating increased to 138 pounds.
The ranking of Prince Khalid Abdullah's unbeaten, 10-time winner is only bettered by the same owner's Dancing Brave, which ranked 141 in 1986.
"I do think he can go even higher," Gardiner-Hill said.
"I do suspect he can be a 140-horse, it just depends if he gets the opportunity."
The World Thoroughbred Rankings scale has been lowered slightly since 1986, meaning Frankel could be ranked similar to Dancing Brave.
His rating, which still has to be ratified by Gardiner-Hill's international colleagues, is two pounds higher than last year, moving him above Peintre Celebre and Generous on 137 and Sea The Stars on 136.
Trainer Sir Henry Cecil wants Frankel's next outing to be the Queen Anne at Ascot and told his official website: "Over the last two seasons he has come on a good deal from his first race and hopefully he will do the same this season."