The most common and most likely answer to this crossword clue is the 10 letter word TOE-TO-TOE
I've seen this crossword clue in Financial Times
T
O
E
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T
O
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T
O
E
More clues leading to the result TOE-TO-TOE
Buddy explains!
The straight part
We know that "In close combat" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case in close combat = toe-to-toe.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.