The former Spartak Moscow keeper admitted it was "a surprise" to see the Blancos captain dropped, but feels the number of games played in recent seasons may have taken its toll
Jose Mourinho controversially dropped the Blancos captain for the 3-2 defeat by Malaga, citing the move to play Antonio Adan as a "purely technical decision" amidst widespread criticism from club officials and supporters.
Although the former USSR intermational admits the decision to leave out the Spain icon came as a shock, he feels the number of matches he has played over recent seasons could perhaps be taking its toll on the player.
The 55-year-old told AS: "Of course it was a surprise. Casillas is a very good goalkeeper.
"Maybe [he is] a bit tired after playing so many club and international games in the past few seasons. The Spanish league, the Champions League, the World Cup, the European Championships - that's a lot of tournaments."
Mourinho came under fire for the decision to start Adan ahead of Casillas in the defeat to Manuel Pellegrini's men, although the skipper himself accepted the cut as a footballing decision.
Spartak Moscow legend Dasayev, a runner-up at the 1988 European championships, spent three seasons playing in La Liga with Sevilla shortly before his retirment in 1991.