This easiest way to do this one:
I started a new career, Started a new game, I used the Australian league as it the fewest teams.
Start a career as a player, I picked sydney.
I created a player and put all his stats to 99 (I used a keeper)
Then i went to the calender and stopped the game from processing the results by pressing B. I then Pressed LT or RT and went to the end of the season and press A. This then skipped the whole season.
I did this four times and stayed with sydeny FC each season, doing this I unlocked the following Achievements in this order.
Established Keeper (50)
Play a season as a Goalkeeper in Career Mode
Become a Legend as a player in Career Mode
Then after 3rd season, this unlocked.
It's in the Blood! (25)
Go from being a Player to the Manager (or Player Manager) in Career Mode
as I was asked to be player manager.