The most common and most likely answer to this crossword clue is the 7 letter word HARD-ON
H
A
R
D
-
O
N
Buddy explains!

The straight part
We know that "without this, (it would) certainly (be difficult to perform, sexually)" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case without this, (it would) certainly (be difficult to perform, sexually) = hard-on.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.
What does HARD-ON mean?
HARD-ON noun- An erection of the penis.