The man who killed four people with a semi-automatic rifle while rampaging through a Midtown Manhattan office tower carried a note with him that appeared to blame the National Football League for his degenerative brain disease,

An NFL employee was seriously injured during the mass shooting at the Manhattan office tower that houses the league’s headquarters.

Shane Tamura, the Park Ave. gunman who killed an NYPD officer and three others before taking his own life, left behind a suicide note saying he suffered from CTE, a brain injury often linked to playing football, and was targeting the NFL — but took the wrong elevator, officials said Tuesday.