Fernando Torres will join Milan permanently on January 5 ahead of his expected return to Atletico Madrid.
Liverpool boss Brendan Rodgers has insisted Mario Balotelli will not be going out on loan in the January transfer window.
The 25-year-old has spent the last month on loan at Sheffield United, for whom he has made five appearances, with his spell at Bramall Lane scheduled to expire on Tuesday.
A brief Leeds statement read: "Leeds United can confirm that Ryan Hall has been suspended from the club pending an investigation into a disciplinary issue.
"No further comment will be made at this stage."
Hall arrived at Leeds from Southend in October last year when Neil Warnock was in charge at Elland Road.
The former Crystal Palace trainee made only two starts and three substitute appearances for Leeds last season and has failed to appear for the first team during the current campaign.
While at Palace, where he featured only once for the first team, Hall had loan spells at Dagenham and Crawley before joining non-league Bromley. He signed for Southend in July 2010 and made over 100 appearances in total for the Shrimpers.