Messi missed Thursday's semi-final against Guangzhou Evergrande because of pain caused by a kidney stone and Neymar was recovering from a small strain in his adductor muscle.
"The two are improving," said Luis Enrique without giving further details.
Team captain Andres Iniesta added. "They haven't been able to train and it will depend on how their sensations, I hope they can play.”
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European champions Barcelona meet River, their South American counterparts, on Sunday.
Messi never played professionally in Argentina and has faced an Argentine side only once before, when Barcelona met Estudiantes in the 2009 final.
(editing by Justin Palmer)
