Tottenham midfielder Eric Dier and Manchester United defender Phil Jones are the leading candidates to captain England against Germany.
Cahill was one of the few options remaining to skipper the side for the high profile friendly at Wembley, but missed training with a suspected back injury on Thursday.
The Chelsea defender is now regarded as a major doubt having sat out of Southgate's final session with his squad this morning.
The 31-year-old only reported for duty on Tuesday, a day after the rest of the players, having stayed behind at Chelsea to be assessed by their medical department. He sustained a knock during the 1-0 win over Manchester United on Sunday.
One of Southgate's captain candidates would normally be Joe Hart, but the West Ham keeper is set to be dropped in order for Jack Butland to be given a chance to impress.
The England coach has also intimated that Manchester City defender John Stones, who faced the media today, isn't getting the armband either.
That leaves Dier and Jones as the most likely squad members to receive the honour.
