Preparing for the Boxing Day Test at the MCG, the Australians were in the wars on Tuesday - with all-rounder Watson wearing a James Pattinson delivery on his helmet, while Mitchell Starc edged onto his left knee in further cause for concern.
Most notably, though, Watson's head knock was similar to that of Phillip Hughes, who died from injuries sustained when hit in the head during a Sheffield Shield match in November.
Haddin, who retains the vice-captaincy in Michael Clarke's absence, said Watson pulled up fine, but was "shaken".
"I had a chat to him - he's a bit shaken, but he's OK," Haddin said.
"It's just getting hit in the head - he's just a bit shaken.
"He's shaken as anyone would be. I can't really go into any more details because there's no more details to give."
Victorian quick Pattinson was also visibly moved by his involvement, while Watson later shirked a public appearance for Cricket Australia's Family Day in order to rest after the incident.
Haddin also said Starc had pulled up OK, and would be fit for selection - albeit he is tipped to miss out for the Test, starting Friday, due to the returning Ryan Harris.
"I think he's trying to get out of having to bowl," Haddin joked of Starc's knock in the nets.
"He's alright. He just hit the ball onto the inside of his knee."