Pitt got a wedding licence at the end of last month, which stated they must marry in 90 days.
The deadline could see the big day for the pair clash with the nuptials of Aniston, which would spark a bitter fight over celeb guests, reported Sun online.
"Brad and Angelina left themselves short of time to sort out their wedding because of the licence deadline. A few months is nothing when you're planning a wedding - especially one as major as theirs.
Aniston is finalising her plans to walk down the aisle with screenwriter fiance Theroux. There was talk she would go to Pitt's wedding, despite him leaving her for Jolie.
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"All that goodwill would go out the window if Brad's wedding date comes close to hers. Jennifer will see it as an attempt to upstage her and there will be a battle over Hollywood guests. She knows they will be judged on who had the better wedding by pulling in the biggest stars," the source added.
Pitt and Jolie are said to have their hearts set on marrying at the chapel on their 35 million pound Chateau Miraval estate in France - where their wine is produced.