The 18-year-old trained with the team on Monday but has not been given the all-clear to play by club medical staff.
It is expected that a decision about his inclusion in the team for the final will be made after Barcelona train at the Stade de France on Tuesday.
Messi tore a thigh muscle during the second leg of his side's Champions League knockout tie against Chelsea on March 7.
"The fact that Messi will be with us will make us stronger but we don't know if he will play in the final," Barca midfielder Deco told a news conference at the Nou Camp.
Deco, the only member of the present Barca squad to have won the European Cup after helping Porto lift the trophy in 2004, played down Barcelona's favourites tag.
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"We can't say we are the better team and even if we were it wouldn't guarantee us victory. If you don't respect your opponents things can start going wrong.
"(AC) Milan were winning 3-0 last year against Liverpool and ended up losing in the end. We need to be serious, calm and fully concentrated so that we don't make any errors."