Is sure to be injured — athlete's back put out again (7)
I believe the answer is:
Here is my best explanation:
'put out again' is the definition.
('issue' can be a synonym for 'put out' so perhaps 'reissue' is OK for 'put out again')
'is sure to be injured athlete's back' is the wordplay.
'to be injured' is an anagram indicator.
'back' says to take the final letters.
The last letter of 'athlete' is 'e'.
'issure' anagrammed gives 'reissu'.