The Robins rejected a £2million bid from Championship rivals Wolves for the 24-year-old in January while Blackburn, Portsmouth and Wigan have also been linked with the former Millwall man.
Chairman Lansdown told the Evening Post: "Marvin is contracted to Bristol City Football Club and we turned down a £2million bid from Wolves in January, only for Marvin to be injured the following week and to be out for a critical part of the season.
"He is a key part of our squad and as far as I am concerned he will be here. But who knows in the transfer window? Things happen and every player has got his price.
"If a Premier League club comes along for Marvin and offers the right money then it is going to be very difficult for us to stand in his way.
"Those are the practicalities of football and we have to live with those and deal with them when they come along."