Police have offered support to referee Michael Oliver and his wife Lucy and warned social media trolls they could be committing a criminal offence by abusing them.
The couple have been targeted in the wake of last Wednesday night's Champions League quarter-final, second-leg clash between Real Madrid and Juventus, during which Northumberland match official Oliver awarded a disputed stoppage-time penalty from which the Spaniards won the tie.
A Northumbria Police spokesperson said: "We are aware of threatening messages being posted on social media. This type of behaviour is completely unacceptable and those writing the messages need to be aware that they could be committing a criminal offence.
"Neighbourhood officers are in touch with the victims in this case to offer them support and ensure any further offences are reported to police."
The Professional Game Match Officials Limited (PGMOL) condemned the abusive messages aimed at the pair, while Twitter confirmed that it had removed a series of tweets from its platform over the weekend.
Oliver, 33, initially found himself in the firing line when Juventus keeper Gianluigi Buffon, who was sent off after he protested furiously against the penalty decision, hit out in a post-match interview.
Buffon, whose side had fought back from a 3-0 first-leg advantage to level the aggregate score at 3-3 at the Bernabeu Stadium before being beaten by Cristiano Ronaldo's last-gasp spot-kick, said the referee had a "bag of rubbish for a heart" and stood by his claims at the weekend.
Oliver was fourth official at Saturday's Premier League match between Huddersfield and Watford and was due to take charge of West Ham's Premier League clash with Stoke this evening.
His wife is also a referee, officiating in the Women's Super League and men's non-league matches.