The nineteen-year-old younger brother of Liverpool's John Arne Riise, trained with City back in February and Keegan seemed set to sign the player from Norwegian club Aalesund, but the deal did not materialise.
"Bjorn Jelge Riise is one of the trialists who will be coming back. I have just organised it," Keegan told the club's official website.
"He has been playing on loan with Viking Stavanger and is a free transfer now. He will be back for ten days with a view to us looking at offering him a contract.
"We tried Simon Colisomo and it didn't work. As we get to see people go out we still have to put out what we think is a decent reserve side and the balance of that has got to be right."
"We probably have too many central defenders at the moment. Paul Ritchie is on loan and that comes to an end at Christmas so he will be back here. So we have to make sure that when we fetch these players in we can give them games."
"We don't want to bring them in to loan them out, as we have already sent some of our players out on loan for experience at a better level than we can give them, players like Stephen Jordan."