The Turkey star is certain the two Liga giants will challenge for the Champions League next season as he believes Spain is still the dominant force in football.
Tito Vilanova's side was humbled 7-0 on aggregate by eventual winner Bayern Munich in last season's semifinal, while los Blancos were edged out 4-3 by Sahin's side.
However, the former Madrid midfielder believes both Liga giants will be gunning for glory next season having been wounded by the manner of their exits from last season's competition.
"The Spaniards were hurt by getting eliminated in the semi-finals," the 24-year-old told Kicker. "This will prompt a reaction and I'm sure that Real Madrid and Barcelona will come back very strong this season."
Despite the impressive form of Bayern and Dortmund last term, Sahin believes Spanish football is still the strongest force in Europe - but believes the Bundesliga is fast catching up.
"For me, the Spaniards are still the number one," he added. "They have dominated European football for the past six to eight years.
"However, the Bundesliga is on the right path. We will keep on playing a major role in the coming years."
Jurgen Klopp's men are currently preparing for the Supercup final against Bayern on July 27.