Ferguson was involved in the World Cup qualifiers on Friday, and he came off with an injury during Northern Ireland’s incident-packed 4-2 defeat by Portugal at Windsor Park.
Ferguson was clearly in discomfort when he had to be substituted in the 76th minute.
Northern Ireland manager Michael O’Neill has rated him doubtful for their next Group F qualifier in Luxembourg on Tuesday.
And Lee Clark will be concerned as Ferguson has only just recovered full fitness for Blues after a groin problem.
The Newcastle United loanee was sidelined for Blues’ Capital One Cup victory at Yeovil Town after being withdrawn in the Leicester City game.
And he was introduced as a 57th-minute substitute against Ipswich Town as Clark went with Paul Robinson to start in the left-back role.
Ferguson is an important player for Blues because of his versatility on the left-hand side.
He was re-signed on loan from the Toon because he is adept at either wing-back, left-back or wide left of midfield.