Millwall have signed former Brighton & Hove Albion goalkeeper John Sullivan on a one-year contract.
The 21-year-old was allowed to leave the Seagulls at the end of the season, having made 17 first-team appearances for the club.
He told his new club's website: "I'm excited at the prospect of trying to get into the first team next year.
"It's a great chance to come to a big club like Millwall that should be in the Championship.
"Hopefully next year we can try and have another go at getting back to that level."