Sorry for the confusion. I have no idea about what he has with us although it would not be a surprise if there was a clause (but it would be a lot higher than £3 million I imagine).
Gross had a relegation clause in his contract from memory so when Ingolstadt went down, he could leave for only £3 million (or something like that). Given he had created the most chances in the Bundesliga the previous season, I imagine he would have cost significantly more without the clause.
Stats like that illustrate how ridiculous the English market is (although I realise Gross would have cost more without that relegation clause in his contract)