Birmingham have agreed a £2.2m deal to sign Brentford's Harlee Dean and also want Bristol City's Aden Flint, Sky Sports News understands.
Dean has left the Bees' training ground in west London and is on his way to the Blues to undergo a medical and finalise personal terms.
Sky sources also understand Birmingham have seen a £3.5m offer for 28-year-old centre-back Flint rejected.
Flint, who has only made two appearances for the Robins this season, is also of interest to Norwich City but they are yet to make a formal offer.
Dean has entered the last year of his Brentford contract and has been unable to agree to new terms. The fee agreed with Birmingham also contains a number of potential add-ons.
The 26-year-old was suspended for the opening game of the season at Sheffield United but has started the club's last three league games.