Watson put the finishing touch on the Hawks' hard-fought 14.15 (99) to 13.4 (82) win at the MCG on Thursday night with a close-range goal after the siren.
The 21-year-old was then involved in an animated exchange with fans behind the goals at the city end of the ground, where the Swans' cheer squad was situated.
An AAP photograph taken at the time shows a liquid-filled Coca-Cola bottle narrowly missing Hawks players.
"They were throwing Coke Zero cans out there ... I saw one just go straight past me," Watson told Nova 100 on Friday.
"I dunno what happened with the guy but ... it just landed right next to us.
"Lucky it didn't hit any players, but yeah, a few players saw it. I mean, I was giving them heaps, but I'm not sure a Coke Zero bottle to the face in return would've been nice."
In a statement on Friday, the AFL confirmed the involvement of Victoria Police and said it is working with the MCG to investigate the matter.
"The alleged offender was not from the Swans cheer squad and his identity is currently unknown," the league said.
"We have the best fans in the world, but throwing objects at players will never be acceptable and if caught you will lose the privilege of being able to attend the footy.
"Victoria Police will now investigate the matter with assistance from the MCG, which will provide all relevant information."
A cult hero for Hawks supporters as well as one of the AFL's renowned agitators, Watson regularly engages with fans on the other side of the fence.
"It's good for the game. I feel like people like it," he said.
"Sometimes in a close game like that it's a bit of fun."
Watson shook off heavy knocks to his hip and head in the third quarter, playing a key role as Hawthorn overran Sydney with 5.5 to 1.1 in the final term.
Both sides are among the 10 teams facing an early-season bye after featuring in Opening Round this month.
The Hawks have an 18-day break before their next outing, in the traditional Easter Monday clash with Geelong.
"We'll not say it's a disadvantage because we don't want to have that mentality," Watson said.
"But people can lose momentum, which is annoying. It's so weird having a bye this early.
"I liked it (Opening Round) because we played in it, but I'm not fussed if it goes out of the game either."
