The 23-year-old has made an impressive start to the season and signed a new contract with the club last month, that will keep him at The Riverside until 2015.
“Were there any bids for Marvin? No. Were there any enquiries? There were a few, but the bottom line is he’s not for sale,” said Mowbray.
“He’s just signed a four-year deal. Marvin’s a lovely lad who’s enjoying his life here at the moment. He wants to come to training with a smile on his face and if he stays fit and continues his high level of performance he’s going to play.
“I think with Marvin, I don’t think it was in my mind really (to sell him) but I think it’s good that people enquire about your players.
“To get to the point where from a year ago, Marvin didn’t have a squad number and was sent out on loan to have some pretty decent football clubs enquire about him is great credit to Marvin. But we didn’t need to sell.
“We’ll see at the end of the season whether or not Marvin is a goalscoring centre-forward. If he is then no doubt in another 12 months’ time if he doesn’t match it I’ll be asked if he was a flash in the pan.
“We’ll wait and see – I’m sure Marvin will have in his own mind how many goals he wants to score this season.”
