Birmingham will travel to Maribor in the UEFA Europa League on Thursday without injured defenders Stephen Carr and Curtis Davies.
Carr (knee) and Davies (bruised leg) both picked up knocks in last Saturday's 1-1 home draw with Barnsley.
Manager Chris Hughton, who will include Luke Hubbins and Akwasi Asante in his 20-man squad for the trip to Slovenia, is expected to hand Jonathan Spector a start at right-back in place of Carr, with Pablo Ibanez in contention for Davies' central defensive role.
Hughton said: "I think Curtis is touch and go for Sunday [at Nottingham Forest].
"Stephen took a whack on his knee. It's not a major problem, but that too needs a few days to settle down."
Striker Nicola Zigic, who has stepped off the bench for the Blues' last two games, is close to starting his first game since February following groin surgery.