The index will undergo its quarterly reshuffle based on a reading of each firm's market value at the end of trading on Tuesday 11 December.
Experts are predicting that seven firms in total will be axed, one of which being Rock which is likely to then end up in the FTSE 250 index of medium-sized firms.
The BBC has suggested that the places of Daily Mail & General Trust, Tate & Lyle and DSG International are also in jeopardy.
If the bank does lose its place, any investment funds which track the FTSE will be forced to sell their holdings.
Firms which look likely to fill the probable gaps in the FTSE 100 include Burberry, Admiral and Thompson.
Northern Rock's shares stood at 103.8p at 3pm on Wednesday.
