Celtic manager Ronny Deila insists Virgil van Dijk does not want to leave the Scottish Premiership leaders in January.
Celtic boss Ronny Deila says keeping his best players will take priority over acquisitions in the transfer window.
The 29-year-old striker, who began his career with Eredivisie champions Ajax in 2004, spent last season at Heerenveen, where he scored four goals in 13 appearances, but he has been out of action since sustaining a neck injury.
De Ridder, who can play up front, as an attacking midfielder or as a winger, impressed during a recent trial at Mandemakers Stadion and technical manager Janus van Gelder is delighted to add the Dutchman to the RKC squad.
He told the club's official website, rkcwaalwijk.nl: "We are very pleased with the arrival of Daniel.
"He's at his best on the flanks and we currently need cover in that position as we have injury problems.
"What really appeals to us all is the drive that Daniel has.
"He wants to be in Holland to show what he can do.
"We offer him a stage here and in this way we hope to work together in the coming months."
The former Birmingham and Wigan forward spent two seasons at Celta Vigo after leaving Amsterdam and played in Switzerland at Grasshopper before returning to play his football in Holland in 2012.