UEFA rules prevent any player who appears in a playoff from representing another team later in the competition, and Fabregas reportedly might refuse to play against Udinese to preserve his Champions League eligibility for Barcelona.
Arsenal is scheduled to host the first leg on Aug. 16. The return is in Italy on Aug. 24.
Barcelona has pursued Fabregas for more than one year and hopes to sign its former youth player before the transfer window closes Aug. 31.
UEFA required clubs in the playoffs to submit their "A'' list of 25 eligible players by Monday's deadline. Clubs can also select younger homegrown players from a "B'' list.
Fabregas, Arsenal's captain, appears at the top of the official UEFA list followed by Robin van Persie, who is in line to take over the captaincy if the Spain international leaves.
Van Persie is suspended for the home leg against Udinese after being shown a red card as the Gunners were eliminated in the round-of-16 last season by Barcelona.
Arsenal manager Arsene Wenger and midfielder Samir Nasri will also miss the first leg in London. They each received a one-match UEFA ban for "improper conduct" toward referee Massimo Busacca in Barcelona.
Arsenal included Alex Chamberlain on its UEFA "A'' list just hours after completing the purchase of the 17-year-old winger from Southampton for 12 million pounds ($20 million).
Wenger extended his selection options beyond the 25-player limit because first-team regulars Jack Wilshere, Aaron Ramsey and Wojciech Szczesny can be included on the "B'' list. All were born since January 1990 and have been with the club for more than two years.
Fabregas on Arsenal's Champions League squad list
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