The former Spain international has warned that the Spanish champions cannot be underestimated in the Copa del Rey and Champions League
The reigning Spanish champions currently sit only third in the league table, trailing Barca by 15 points, but Rexach believes the Blancos now have the advantage because they can focus on other competitions instead.
"The fact that Real Madrid have nothing to play for in La Liga any more makes them all the more dangerous in the Champions League and Copa del Rey," the 66-year-old told reporters.
Madrid lock horns with the Blaugrana in the semi-finals of the Copa del Rey on Wednesday, with the first leg taking place at the Santiago Bernabeu.
Head coach Jose Mourinho and his men will have to deal with Manchester United in European club football's elite competition.