Milan are keen to keep the 33-year-old England midfielder after he scored two goals in his first four starts but Galaxy have said he must return in March. Beckham has said he is undecided and talks are planned.
The Italian club must decide on their UEFA Cup squad for the remainder of the season after Sunday's Serie A match at Lazio.
"The delivery of the UEFA list will be tomorrow evening before midnight. The possible inclusion of Beckham in the list would simply be our right," Ancelotti told a news conference.
If Beckham leaves in early March, he would be able to play in the away and home legs only of the last 32 tie against Werder Bremen on February 18 and February 26.
The coach did not speculate whether Beckham's possible inclusion in the list would mean he was staying longer. However, he sounded pessimistic when answering another question.
"Even when Beckham leaves, the midfield is covered because we have (Mathieu) Flamini available," Ancelotti added.
Beckham, on loan at Milan for two months to boost his England chances during the U.S. close season, has been named in the squad for Sunday's Lazio game despite carrying a leg muscle injury.
Ancelotti said a final decision on the 33-year-old's fitness would be made before kickoff and he could be restricted to a place on the bench.
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