Herrera denies involvement in match-fixing
The 25-year-old was one of 41 players and coaches named in connection with a case relating to a clash between Levante and Real Zaragoza at the end of La Liga's 2010-11 season.
It is alleged that Levante players were paid to lose the match, which Zaragoza - featuring Herrera - won 2-1.
Herrera, along with Swansea City's Jefferson Montero - who was in the Levante side - have been named, and the United man took to his official Facebook account to protest his innocence.
"I have never had and will never have anything to do with manipulating match results," he said.
"If I am ever called to testify in any judicial hearing, I'll be happy to attend, as my conscience is clear.
"I love football and I believe in fair play, both on and off the pitch."