Riordan has struggled to make an impact at Celtic

The 24-year-old left Edinburgh rivals Hibernian for the SPL champions in June 2006 but has struggled to break into the Parkhead first-team since.

The player's agent says the former Scotland under 21 international is open to all offers.

BBC Scotland also understands the Tynecastle club are willing to increase Riordan's current Celtic wage.

Riordan joined the Parkhead side in a �200,000 deal having previously signed a pre-contract agreement that would have started in January of this year.

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But he seldom appears in the Parkhead side's ranks, making just 19 appearances and scoring four goals.

And Riordan will also be keen to add to his solitary Scotland cap, earned during a friendly against Austria more than two years ago.

Hearts majority shareholder Vladimir Romanov is believed to have made tentative approaches for Riordan before he left Easter Road but was told he would not sign.

However, this is unlikely to prevent Romanov from renewing his interest in the former young player of the year.