Jockey Robert Winston has been released on bail after being arrested by police probing race-fixing allegations.
The 25-year-old, a former champion apprentice, was the fifth jockey to be questioned by the police on the matter and was bailed until early May.
City of London Police said the arrest was "part of the ongoing investigation into fraud in horse racing."
"We anticipate there may be more arrests," said detective chief superintendent Steve Wilmott.
"This is a very involved and complex investigation which has taken time to unravel," he added.
Winston's agent Richard Hale confirmed the arrest of his client, who is currently out of action with tonsilitis, on Wednesday.
A total of 26 people have now been arrested since September and questioned about alleged conspiracy to defraud.
Leading jockey Kieren Fallon was one of 16 people to have been arrested by police in September as part of their investigation.
A further nine were subsequently arrested and all have been bailed to appear at a police station in April.
All the jockeys have so far denied any wrongdoing.