Blackwell is working with the club's administrator through the January transfer window as the Hatters' top players are sold to raise funds.
At the age of 22, Luton-born Brill is the number 1 at Kenilworth Road. Tomorrow's game at Anfield will be his 50th for the club in all competitions. He also made 8 appearances on loan at Gillingham a year ago.
City require a keeper to compete with Boaz Myhill due to the current unavailability of Matt Duke.