كتب : Hatem Maher
Malian midfielder Diarra missed Real's 2-1 victory over arch-rivals Atletico Madrid last Saturday after injuring his knee while on international duty.
Fellow midfielder Guti was also absent due to a muscle strain.
But both men have fully recovered and are ready to face Bilbao in Sunday's game at Santiago Bernabeu, Real said on their official website.
Los Merengues will miss prolific striker Ruud van Nistelrooy, who is out through suspension.
Forward Gonzalo Higuain, who scored the winner against Atletico, is expected to fill in for the Dutchman.
Defending champions Real are fifth in the league table on 16 points, three adrift of leaders Valencia.