The 30-year-old has signed a deal that will keep him at St. Andrew's until 1 January, 2014.
Blues have been left light in their forward ranks, following the recent season-ending knee injury sustained by Matt Green
McLean began his career at Leyton Orient, before having spells at Aldershot Town and Grays Athletic. A move to Peterborough followed, where he was a prolific scorer with 83 goals in 188 appearances, which helped the Posh to back-to-back promotions.
He left London Road to join Hull in 2011 and has subsequently made 83 appearances - scoring 12 times. He spent a short spell out on loan at Championship side Ipswich Town last season.
McLean will wear first-team squad number 35 and is expected to be available for Saturday's visit of Blackpool (3pm kick-off).