The Premier League's main concern is the bottom line (6)
I believe the answer is:
footer
'the premier league's main concern is' is the definition.
I can't judge whether this definition defines the answer.
'bottom line' is the wordplay.
'bottom' becomes 'foot' (foot is a kind of bottom).
'line' becomes 'er' (I am not sure about this - if you are sure you should believe this answer much more).
'foot'+'er'='FOOTER'
'the' acts as a link.
Can you help me to learn more?
(Other definitions for footer that I've seen before include "Text at the page bottom" , "10 [OBELI] appear here" .)