The singer, who recently picked up his 18th Brit honour, reveals he was "stoned" when he asked his manager to send the Manchester United hero his award in the hope it would cheer him up as he recovered from an injury.
"Wayne got injured in a match, and I shouted to my manager... 'Michael, will you send a Brit to Wayne Rooney... Tell him to get better from me...'," Robbie tells the Radio Times.
"It was like those shopping decisions you make on Amazon (shopping website) when you're on Ambien (sleeping pill). But it was well intentioned, and he sent me a pair of signed football boots. So, good deal!"
But he tells the publication he doesn't always get feedback when he reaches out to celebrities he admires, adding, "Last year I tried to work with Bruno Mars (but) didn't hear anything back. (I) tried to work with (Swedish hitmaker) Max Martin - didn't hear anything back. They literally didn't return my calls.
"Then I met Harry Styles in an airport (and said), 'Oh, you're writing, Harry? Great, who with?' He goes, 'Well, I just spent a week with Bruno Mars, and I'm about to spend a week with Max Martin'."
Robbie picked up his latest Brit honour earlier this month (Nov16), when his old Take That bandmates presented him with the Brit Icon award during a gig in London. Williams is only the third artist to receive the trophy, which has also been given to Sir Elton John and David Bowie.