According to The Sun, the Magpies have been joined by Bayern Munich in monitoring the forward's progress at the Bundesliga outfit, where the 27-year-old has scored 102 goals in 179 appearances.
Hoffenheim sporting director Alexander Rosen told German publication TZ that offers below the £44m mark will be rejected.
"I never rule out anything, that's not in our business," Rosen said. "We had an offer of €30m (£26.3m) for Andrej from Italy during the winter the break.
"That was not an option for us. But what happens if €50m (£43.7m) are bid, I cannot say."
Kramaric, who is currently at the World Cup with Croatia, featured in his country's 2-0 win over Nigeria last Saturday.