The team said Sunday that Riley informed the club of the threats and did not know who made them. The team has notified the league's security department.
Cooper was fined by the Eagles after his slur became known Wednesday. He left the team Friday to seek counseling.
"Riley Cooper made us aware of the tweets when the video became public," the team said in a statement. "He told us that he did not know about the video. He informed us he blocked the tweets because he did not know the person nor understand the context of what that person was threatening.
"We promptly alerted NFL security. This information potentially speaks to a legal issue that is a matter between Riley and the authorities. Our focus has been on Riley's words and actions."
The video of Cooper was taken at a Kenny Chesney concert in June. Cooper apologized profusely both Wednesday and Thursday.
Eagles coach Chip Kelly has said Cooper's roster spot is not in jeopardy. Cooper has just 46 catches and five touchdowns in three years with the Eagles, but had been practicing with the starters after Jeremy Maclin's season-ending knee injury.
Asked when Cooper will return to the Eagles, Kelly said there's no time frame.
"When we do, we'll make sure we announce it so it's not going to be a surprise to anybody," Kelly said.
Cooper's departure coupled with Maclin's injury leaves the Eagles lacking experienced receivers behind two-time Pro Bowl wideout DeSean Jackson and longtime slot receiver Jason Avant. It's giving Ifeanyi Momah and Arrelious Benn a chance to not only make the team, but get some playing time.
Benn was the 39th overall pick by Tampa Bay in the 2010 NFL draft. He had 59 catches and TDs in three seasons with the Buccaneers.
"Football is all about opportunity and timing," Benn said. "The next guy has to step up and have that next-guy mentality. You have to know what you have to do and do it."
Momah, a 6-foot-7 receiver out of Boston College, hasn't played since tearing a knee ligament in the first game of his senior year in 2011.
"Right now, I'm not looking at the depth chart," he said. "I'm going to work the same way whether I'm with the first team or last team. I'm just trying to be consistent and work hard every play, establish myself as a hard worker and prove I can be an every down receiver. I'm reaching levels I've never reached before."
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