The 30-year-old American has been replaced by 39-year-old veteran Shay Given who has made only three Premier League starts in three seasons.
Sherwood said: "We have not closed the book on Brad and Shay realises that. Who knows if he will play in the cup final or not? I might have swung it round by then.
"I spoke to Brad and said I would play Shay. And I expect him to have the same attitude as Shay and that's exactly what I've got from him.
"His attitude has been fantastic. The door is not closed for Brad Guzan. It's life and football."