Report from BBC Sport: http://www.bbc.co.uk/sport/football/40980955
Cardiff City have launched a fresh investigation into the signing of Andreas Cornelius in July 2013.
The Danish striker, then 20, arrived for a club record fee of an initial £7.5m but failed to score in 11 games.
Cardiff owner Vincent Tan believes the club paid too much - and has instructed lawyers to take a detailed look into the transfer. Tan says he has new information on the matter.
It comes as Tan renewed his attack on former boss Malky Mackay.
Tan called Mackay an "idiot" over the Cornelius signing.
The striker was Scotsman Mackay's first purchase after guiding Cardiff to promotion to the Premier League, but he rejoined FC Copenhagen after just six months in Wales.
Cornelius rediscovered his form at Copenhagen with a tally of 45 goals over his two spells with the club.
Cornelius joined Italian Serie A side Atalanta this summer.
"It was unfortunate that we only stayed in the Premier League for one season," said Tan.
"You know the main reason, I always say, and I have told Mehmet [Dalman, Cardiff's chairman] the same, is that we spent a lot of money there - I think it was £50m.
"What did we get? We paid £10.5m [based on add-ons] for Cornelius who didn't even play 45 minutes and then the manager said he was a project.
"I'm in the Premier League, I need to survive. What an idiot he [Mackay] is."
Tan added, "You pay for a big striker £10.5m you should play him 90 minutes, not 45 minutes, five minutes, 10 minutes. Because he's a project he [Mackay] says, finally, he says he [Cornelius] is a project.
"How come I'm in the Premier League and you're finding time to do a project for the future? What rubbish is that? And you pay £45,000 a week for a project? Rubbish!"
Chris Nott, a senior partner at Cardiff law firm Capital Law, confirmed he's been instructed to look into the Cornelius transfer.
"Mr Tan has asked for this particular transfer to be looked at in micro detail," said Nott.
Mackay's representatives told BBC Wales Sport they had nothing to say regarding the new investigation.
Tan's acrimonious sacking of Mackay - who is now the Scottish Football Association's performance director - was one of several flashpoints in what has been a tumultuous tenure since the Malaysian businessman bought the Welsh club in 2010.
Cardiff subsequently sent a dossier to the Football Association alleging that Mackay and former head of recruitment Iain Moody shared racist and sexist texts, with the governing body deciding that both men would face no action.
The club engaged law firm Mishcon de Reya, whose investigators obtained a search order from the High Court to enter the property seizing work computers and phones and taking electronic imagery of evidence.