Not for sure but could be the start of bud rot… what’s your humidity like? What does that spot feel like? bud rot is soft and mushy I believe and spreads very fast!
I haven’t yet had to deal with bud rot but I am able to maintain about 30 RH in my grow room during flower and plenty of canopy maintenance with good airflow can solve it for your next cycle!
Humidity is 42 at the minute 45 is the highest it gets when lights are on. It does feel kind of mushy, in comparison to the rest of the bud. Could I chop the top off and try save the rest? Or would it have already spread?
Definitely may invest in some more airflow, have a feeling this may be the problem 
Yeah, looks like to me as well. Please answer the q’s to be able to help better.
In general if RH is below 45% the chances of bud rot go way down.
I would remove affected plant material carefully, until you reach green plant material. Then spray down the entire plant with 1/4 cup of 3% peroxide into a quart of distilled water and spray the plant down with that. Then get some fans blowing on the plant. You almost can’t have too much airflow.
The highest it would be at is 45 percent, when its warm and lights are on. I have maintained a 30 to 40 percent humidity throughout
Must read in to peroxide and spraying, thank you so much!
If temps drop during the dark cycle the humidity will go up.
The spike at lights out can be brutal. My dehumidifier kicked off and it shot up to 70%
I have invested in a heater go regulate the temp throughout