The Dutch winger has had a solid season in Belgium where he scored nine times and registered 14 assists in all competitions for Club Brugge.
Lang has been on the radar of several clubs in Europe since last summer when Club Brugge took up the option to sign him on a permanent deal from Ajax.
West Ham have been keeping tabs on him with a view to taking him to the London Stadium and Serie A giants AC Milan have also been in talks to sign the winger.
And it has been claimed that Club Brugge have set a certain asking price for Lang ahead of the summer.
The Belgian giants want a fee in the region of €30m before agreeing to sell the player in the coming months.
Club Brugge are aware that they are likely to find it hard to resist selling him due to interest from big clubs in Europe.
They want a big profit on the €6m they paid to sign him from Ajax on a permanent deal last year.