Tchaikovsky considered Sapelnikov a great talent and helped him launch his performing career, particularly in Europe.
However, there is not evidence whatsoever to suggest anything of the kind -- a conclusion that anyone who took the trouble to study Tchaikovsky's correspondence would arrive at.
"[7] Sapellnikoff first appeared in England in 1889 playing the Tchaikovsky concerto at a Royal Philharmonic Society concert, under the composer's baton.
He became a favourite at Philharmonic concerts, and created a furore in 1892 by his performance of Franz Liszt's E-flat Concerto, accepting a second engagement for the same season.
In December 1912 he gave Frédéric Chopin's E minor Concerto, under Percy Pitt: in January 1914 the Rachmaninoff again, under Willem Mengelberg: in November 1914 the Liszt A major Concerto, under Thomas Beecham, a performance repeated in January 1915; and the Second Suite by Rachmaninoff (for two pianofortes) with Simeon Rumschisky in December 1915.
[8] In England he amazed George Bernard Shaw with his playing of the octave left-hand passages in Chopin's Polonaise in A-flat Heroic.
Shaw referred to his left-hand playing as "a marvel even among right hands for delicacy of touch and independence and swiftness of action".