An employee of the NFL has been hospitalized after suffering “serious injuries” during a fatal shooting incident at the New York City building where the league is headquartered.

The gunman, identified as Shane Tamura, a 27-year-old licensed private investigator from Las Vegas, opened fire on Monday night at 345 Park Avenue in Midtown Manhattan, resulting in the deaths of four individuals.

Beginning his violent attack in the lobby by wounding an NYPD officer in the back, Tamura then proceeded to the 33rd-floor offices of Rudin Management, where he continued discharging his M4 rifle, ultimately claiming four lives.

As well as Rudin Management and investment management company Blackstone, the building at 345 Park Avenue is also home to the NFL headquarters, which is located on the fifth floor.

In a letter to employees on Monday night, as seen by DailyMail.com, NFL Commissioner Roger Goodell announced that a league staffer is stable in hospital after being ‘seriously injured in this attack.’

‘NFL staff are at the hospital and we are supporting his family,’ his letter added.

Goodell said that the NFL believes all other employees are otherwise safe and accounted for, and the building has nearly been cleared.

‘We are deeply grateful to the law enforcement officers who responded to this threat quickly and decisively and to Officer Islam, who gave his life to protect others,’ he stressed.

NFL employees who work at 345 Park Avenue were also told they should work remotely on Wednesday, but they are also free to take the day off if preferred.

Goodell also reassured them that there will be an increased security presence at the building in the days and weeks to come.

‘Every one of you is a valued member of the NFL family. We will get through this together,’ he signed off the letter.

Sources confirmed Tamura did not enter the fifth floor at the building, yet investigators are looking into into whether his motive was to target the NFL’s offices given his past as a high-school football standout for Granada Hills Charter and Golden Valley in California. 

While he resided in Las Vegas, Tamura spent his high-school years in Los Angeles. He graduated from Granada Hills Charter, a Los Angeles Unified School District school located in the heart of the San Fernando Valley, in 2016. Prior to that he attended Golden Valley, which is further north in the Santa Clarita Valley.

According to high-school sports statistics websites MaxPreps and Hudl, he operated as a defensive back, running back and halfback throughout his career in junior varsity with both schools. 

It is unclear whether his football career continued after he graduated from Granada Hills Charter in 2016. DailyMail.com has approached the school’s athletics department for comment.  

 NFL employees were urged to ‘hide’ after Tamura stormed into the building and opened fire in both the lobby and the 33rd floor.

According to ESPN’s Jeff Darlington, a security alert sent to the league’s employees read: ‘Do not exit the building. Secure your location and hide until law enforcement clears your floor. Please switch phones to silent.’

Photos posted online showed Tamura wearing a sport coat and button-down shirt while carrying the large rifle near the offices in Midtown Manhattan.

He had a silencer on his massive weapon when he opened fire inside the lobby at around 6.30pm, with approximately 30 people inside.