According to reports from Reuters, the Valencia-based holiday property company is currently negotiating a €150m loan from its creditors, Lehman, after falling behind on debt payments, but has yet to secure its financial future.
The news puts a question mark over Grupo Llanera's shirt sponsorship deals with Charlton Athletic FC, which signed a £6.6m deal with Llanera in December 2005, and London Irish, which has a £2m on-shirt deal with the Spanish firm.
London Irish confirmed it was fully aware of Grupo Llanera's financial difficulties, but said it was continuing its business relationship with the company.
A spokesman for London Irish said: "[Grupo Llanera] is working to secure its financial situation and they are honouring their sponsorship commitment to London Irish. In turn, we are honouring the deal we have with them."
The Guinness Premiership side signed a £2m three-year deal in July last year that extends to shirt sponsorship, as well as support for the club's amateur and community programmes.
Fernando Gallego, chief executive of Grupo Llanera, told the Financial Times on Monday: "Last week we had a temporary liquidity problem, but we are resolving it. We had €2m of missed payments, but we are now getting money back to our suppliers."
If Grupo Llanera's sponsorship of the two clubs were to be pulled, it would mark the second time that Charlton Athletic had encountered problems with a major sponsor in recent times. The Championship side's previous kit sponsor All:sports went into administration in September 2005, midway through a £3m deal.
It is understood that Grupo Llanera's financial difficulties stem from a downturn in the Spanish property market and a global credit squeeze, which has led the company to reduce staff levels to lower its overheads.
Charlton Athletic FC was unavailable for comment.