Replacing SCSI drive in Raid 5 set

I have a Poweredge 2400 with 4 - 18Gb SCSI HDD's in a RAID 5 set installed  in it. One of the drives has failed and I have a new SCSI drive installed. When I attempt to initialize the new disk (through the FAST utility) I get a message of "Initializing will cause all current data, including any existing containers, to be lost, do you want to continue". If I initialize this drive is it going to attempt to rebuild my RAID 5 set? Will I be scrubbing the current container? (this would be very bad....), or is this drive not part of the RAID set yet? thx, for any help in advance.

L_4