The most common and most likely answer to this crossword clue is the 11 letter word CO-DIRECTOR
I've seen this crossword clue in Financial Times
C
O
-
D
I
R
E
C
T
O
R
Buddy explains!
The straight part
We know that "top business partne" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case top business partne = co-director.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.