
Thomas signed a three-year deal when he joined Stoke last summer from Huddersfield Town, having spent the previous season on loan in Ligue 1 with Nantes.
Thomas, who started out at West Ham's academy, was one of Stoke's standout performers last term in what was a disappointing campaign that started promisingly but failed to live up to expectations.
According to transfer specialist Alan Nixon, The Hammers would be likely to stump up the £10m fee that The Potters would be looking for.