A method, apparatus and computer program product are provided to permit a neighbor list to be updated with a detected set cell such that the detected set cell may thereafter be utilized for determining a frequency quality estimate or for inter-frequency measurements and/or considered for inclusion in a virtual active set. From a network perspective, the method may receive information regarding a detected cell that is not on a neighbor list for a user equipment (UE) and that operates at a non-used frequency and may cause a message to be transmitted to the UE adding the detected cell to the neighbor list. From a UE perspective, the method may cause information to be provided regarding a detected cell that is not on a neighbor list and that operates at a non-used frequency and may thereafter receive a message adding the detected cell to the neighbor list.