The 22-year-old has been a revelation since joining from Genk for £8m in the summer and is drawing interest from the likes of Arsenal, Tottenham and Manchester City.
Lambert, however, is adamant that his 18-goal marksman is fully focused on keeping the Villans in the Premier League.
He said: "Christian is playing very well for us and that's the main thing. It doesn't concern me who he is linked with and who he is not linked with.
"It proves he's doing well for me and doing well for himself. That doesn't interest me, what other people think. I don't read the headlines. I just get told.
"As far as I'm concerned, the guy is here and he isn't going anywhere until I say so or not really. That's the bottom line.
"He's a really top lad, really humble and, if he keeps doing what he's doing, he'll be a top, top player.
"The big lad has been phenomenal for us. He is 22, he has got so much to learn and so much to give to the game.
"What he has done for this club, in the short time he has been here, he has got to sustain that, not just over a year - it has got to be for the rest of his career."