Newcastle have revealed that Nicky Butt has a clause in his contract allowing him to return to St James' Park if Birmingham are relegated.
Butt suffered a nightmare spell at Newcastle
He is on loan at struggling Birmingham and Newcastle chairman Freddy Shepherd confirmed the details of his deal.
He said: "Nicky and his advisors insisted on a clause that he would not join Birmingham permanently if they lose their Premiership status."
But Shepherd added: "I am sure this will not be the case."
Birmingham, who travel to Tyneside on Saturday, slipped to 19th in the table
as a result of Saturday's 1-0 home defeat by Everton.
Newcastle will hope they drag themselves out of the relegation zone and are able to fulfil their proposed £2.5m deal for the former Manchester United player, who had a dreadful year at the club following his £2.5m switch from Old Trafford.
Butt was a shadow of the man who starred for England in the 2002 World Cup
Finals and had to issue an apology to fans after leaving the pitch following the
FA Cup semi-final defeat by United without acknowledging them.