Riordan is available on a free transfer as his contract with Hibs expires next week.
Watford and Crystal Palace are among the clubs interested in the highly-rated striker.
Houston Dynamo failed to sign the striker earlier this season, but remain interest in the former Scotland star.
But the Dynamo deny that they have made a new move for the 28-year-old striker.
Dynamo president Chris Canetti told Ontheminute.com: "We had discussions with Riordanís agent prior to the earlier transfer window in April. We were unable to reach an agreement at that time.
"We have remained in contact, but there have not been any formal discussions or proposals about a transfer this summer."