Joachim is out of contract at Coventry City and, with his ability to play wide on the right, his signing would assist United's forward options.
The 29-year-old averaged one goal every two games during his time with former club Aston Villa and his experience will be helpful.
Centre-back Butler, 31, who has made 445 league appearances and won two promotions, has turned down a new deal at Wolves.
Kevin Blackwell is also closing in on another striker and a goalkeeper. He has already confirmed his interest in Fulham forward Barry Hayles and Everton's out-of-contract keeper Paul Gerrard.