Partial Source: The Wrestling Observer Newsletter
It has been confirmed that following his release from TNA, Ric Flair does have a non-compete clause. It has not been revealed how long the clause lasts for, but at this time, Flair cannot sign with WWE.
WWE and TNA are currently involved in a lawsuit and during proceedings for that lawsuit, WWE attorneys told the court that they have no interest in signing Flair. That's not likely the case but it's what they're telling the court.