Pop the loose tees inside with the coin (6)
I believe the answer is:
peseta
'the coin' is the definition.
(I have seen 'Spanish coin' mean 'peseta' so perhaps 'coin' could also mean 'peseta')
'pop the loose tees inside' is the wordplay.
'pop' becomes 'pa' (both can mean father).
'the loose' indicates anagramming the letters (letters are loosened from their original positions).
'inside' indicates putting letters inside.
'tees' is an anagram of 'eset'.
'pa' enclosing 'eset' is 'PESETA'.
'with' is the link.
(Other definitions for peseta that I've seen before include "One hundred centimos" , "Coin from the sea pet" , "Formerly, unit of Spanish money" , "Old Spanish coin" , "Formerly the basic unit of money in Spain" .)