Air carrier Captain reported an NMAC with an unknown object during final approach. No evasive action was taken.

Narrative

Just passed PATRN Intersection Aircraft X was in day VMC conditions in a low light overcast sky; given a 5000' altitude and a heading of 040 by ATC (250 knots and level). The aircraft had just passed the PATRN intersection by approximately 5nm when the Pilot Monitoring visually acquired an unknown object 100 feet to 200 feet below the aircraft at about an 11 o'clock position relative to the heading and saw it on a merge across the nose departing to our 3 o'clock position. The object may have been stationary. A detailed description is not available as the PF; I did not ever visually acquire past a rapid blur under the lower portion of my windscreen. As PM; with Autopilot and Autothrottle engaged; there was no attempt to make any evasive maneuver by the PF First Officer. No targets appeared in that area on TCAS; and no TA or RA was detected.The object is best [described] as an 'orb' shape but distinctly not a quad copter or mylar balloon - due to the speed we both agreed it was mostly a blur with a definite closure angle from 11 oclock departing to the 3 Oclock and below the aircraft; size was estimated to be 8' to 10' across.