The most common and most likely answer to this crossword clue is the 4 plus 2 letter word ODDS ON
I've seen this crossword clue in The Daily Telegraph
O
D
D
S
O
N
More clues leading to the result ODDS ON
Buddy explains!

The straight part
We know that "more than likely" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case more than likely = odds 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 ODDS ON mean?
ODDS ON adjective- Having a chance of winning that is better than even.
- In which the amount won on a bet is less than the amount staked.
- Very likely.