West Midlands Police has now arrested a 47-year-old woman on suspicion of perverting the course of justice.
She remains in police custody as enquiries continue, with officers from West Midlands Police working closely with New Cross Hospital.
A 21-year-old-man detained on Tuesday on suspicion of wounding has been de-arrested and is no longer part of enquiries. Police say no one else is being sought in connection with the crime.
A spokesman for West Midlands Police said: "We have arrested a woman following reports of a staff member being stabbed at New Cross Hospital in Wolverhampton yesterday.
"The 47-year-old woman was arrested just after midday today on suspicion of perverting the course of justice.
"She remains in police custody this afternoon as our enquiries continue to establish exactly what happened and we are working closely with the hospital on this.
"The woman who was hurt in the incident was discharged from hospital yesterday evening following treatment for minor injuries."
An increased police security presence remained at the hospital following the incident.
A nurse who wished to remain anonymous said: "It's quite bad to hear that someone can come on hospital grounds and attack someone as we're here to serve and protect, not be abused.
"I'm just left wondering if there's enough measures in place to help protect people coming into A&E as this is the first time I've known this to happen and I don't want it to happen again.
"I hope she's alright as she's one of us and you don't want to see anyone get hurt like this."