After having his 2015-16 season cut short by injury, the defensive midfielder became a pivotal player for the Belgian giants last term as they won the domestic title and made it to the quarter-finals of the Europa League - losing to Manchester United after extra time.
The 22-year-old remains crucial to Vanhaezebrouck's side and is said to have caught the eye of United, while West Ham are said to be preparing a bid.
But his coach insists it will take a huge offer to persuade the club to sell him this month, although they may be willing to discuss a move at the end of the campaign.
"He can only leave when an insane bid comes in," the Anderlecht boss told Het Laatste Nieuws.
"Over the next six months he has to show his very best level and then we can work towards a top transfer in the summer."
Dendoncker made his Anderlecht debut in 2013 and has since made over 150 appearances for the senior side.
He is currently contracted to the club until June 2021.