"It's science fiction that I have offered him a chance to be my assistant," Lopetegui said of Casillas.
The 36-year-old LA Galaxy striker will call time on his 18-year Ireland career having made a record 145 senior appearances for his country.
Ventura said he needed to look at emerging talent ahead of the next World Cup and wanted to reduce the team's average age.
Wales manager Chris Coleman has confirmed that injured Arsenal midfielder Aaron Ramsey will miss the country's opening World Cup qualifier next month.
Antonio Conte has said only John Terry and Sam Allardyce can decide whether the Chelsea captain should end his self-imposed England exile.
Liam Twomey weighs up the pros and cons of a potential England return for John Terry, who is set to hold talks with Three Lions manager Sam Allardyce.