A 'security incident' during Northampton's Champions Cup win over Cardiff on Sunday is believed to have been a hoax.
Police were called to the Saints' Franklin's Gardens stadium at about 19:00 BST "following threats made on social media".
The game had kicked off at 17:30 and players from both sides left the field straight after the final whistle as a "precautionary measure".
"Enquiries into the incident remain ongoing and we are working closely with both the Saints and our policing partners on the investigation," said a Northamptonshire Police spokeswoman.
Northampton, who won the Champions Cup match 28-12, said they were "sorry that supporters didn't get the opportunity to see the players after the final whistle".
They added: "Following a security incident at the stadium, both sides left the field immediately as a precautionary measure.
"Thank you for your understanding and cooperation.
"The safety of our supporters, players, staff and officials will always remain our top priority."