The most common and most likely answer to this crossword clue is the 11 letter word WHATSISNAME
I've seen this crossword clue in The Guardian
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Buddy explains!
The straight part
We know that "The man I saw’s recollected? No!/The man I saw’s recollected? No!" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case the man i saw’s recollected? no!/the man i saw’s recollected? no! = whatsisname.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 WHATSISNAME mean?
WHATSISNAME noun- A placeholder for the name of a man whose name the speaker cannot remember.