Brattan landed at A-League Men rivals Macarthur and has been a key cog in the Bulls' march towards Sunday's Australia Cup final against Melbourne Victory at AAMI Park.
The 34-year-old enjoyed an impressive campaign last year as Sydney skipper, bravely soldiering on through the pain of a lingering foot issue.
The midfielder revealed he was on the cusp of inking a new deal heading into the A-League All Stars camp but was left shocked when coach Ufuk Talay informed him he was no longer part of Sydney's plans.
"It went back and forth for a good month, and I'd agreed on a contract with the chairman (Scott Barlow) and at the last minute, the coach and technical director changed their mind," Brattan told AAP.
"They said that they wanted to play young players next season, that's fine, that's football and I've been around the game long enough to understand that.
"I thought that I deserved a bit of honesty and if they had said that a month or six weeks before, I would have been fine about it but obviously, for whatever reason, that's what they chose to do.
"It was a very special club to me and a big part of my life and career.
"But I'm happy where I am at the moment and I am excited for the future."
Brattan's arrival at Macarthur has provided the Bulls with instant leadership in the wake of some of the club's most-turbulent months.
Three Macarthur players, including captain Ulises Davila, sent shockwaves through the game after being arrested and charged in relation to spot-fixing claims in May.
"All the boys have really moved on and that (the allegations) is no reflection of the rest of the boys," Brattan said.
"It's been a full focus on the season ahead."
Luke Brattan has already had a big impact at his new club. (Scott Barbour/AAP PHOTOS)
Brattan tipped fellow midfielder Jake Hollman to go to another level at Macarthur this season.
"I think he's got all the attributes to play overseas and while he's still got a lot to learn that will come with game time," Brattan said.
"I'm excited to see what he can do this year because he's a fantastic footballer, a professional and a good kid as well…I'll do my best to help him along."
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