Blues have almost sealed a loan with a view to a permanent move to bring Gardner back to St Andrew’s, Press Association Sport understands.
A deal was close last week and negotiations have continued, with the 30-year-old expected to finalise his switch soon.
Gardner, a Blues fan, played for Birmingham between 2010 and 2011 and helped them win the League Cup during his 18 months at the club.
He signed a new two-year contract at The Hawthorns in October but has not started since August and only made 10 appearances for Tony Pulis’ side this season.
Gardner joined on a free transfer from Sunderland and has made 85 appearances, scoring six goals, for Albion.
Blues have also agreed a £2million deal with Spanish club Granada for midfielder Krhin but are yet to complete the move.
Press Association Sport understands the former Inter Milan midfielder’s family are keen for Krhin to move to Birmingham but he is yet to make his final decision.
The 26-year-old Slovenia international, who has 30 caps, has also played for Bologna and Cordoba.
Blues boss Gianfranco Zola was hopeful of completing a move for Krhin, having been handed £10million to spend in the transfer window.