The Southampton midfielder was one of two players added to the French squad after Franck Ribery and Clement Grenier were forced to withdraw because of injury.
And the uncapped 24-year-old says he almost decided not to answer the telephone call from coach Didier Deschamps.
Deschamps told him on Thursday that he was on stand-by to play in Brazil and 24 hours later confirmed he was needed by his national team.
Schneiderlin said: "I didn't answer the call to start with because I did not recognise the number.
"He told me two players were injured so I needed to be ready and that he would contact me the next day to tell me if I must come.
"After that call, I needed a bit of time before I could sleep because I couldn't stop thinking about what would happen the next day.
"He did not promise me anything, just that I needed to be ready. It was certainly not the easiest night I have had.
"Then Friday, he called me and told me I needed to come. It was an incredible day.
"I can't believe it - everything has happened so quickly."