The Blades captain was sidelined for the second leg because of injury prior to the incident.
A man has been arrested on suspicion of assault after Sheffield United captain Billy Sharp was apparently attacked when Nottingham Forest fans spilled on to the pitch at the end of the Sky Bet Championship play-off semi-final.
Nottinghamshire Police’s chief inspector Paul Hennessy said: “A 31-year-old man has been arrested on suspicion of assault in connection with this incident. He remains in custody and will be questioned by officers.
“Our enquiries into the circumstances surrounding the incident are ongoing. We have spoken to the player concerned and we are working with both clubs who are supporting us with our investigation.”
The Blades captain was sidelined for the second leg because of injury and was stood on the touchline after Forest secured a dramatic 3-2 penalty shootout victory following a 3-3 aggregate draw, which precipitated a pitch invasion at the City Ground.
Footage shared on social media appears to show one supporter running at the 36-year-old former Forest striker and knocking him to the ground.
Forest have condemned the incident and said in a statement they will “will work with the authorities to locate the individual” and the offender will be subject to “a life ban” from the club.