Celtic manager Ronny Deila insists Virgil van Dijk does not want to leave the Scottish Premiership leaders in January.
Celtic boss Ronny Deila says keeping his best players will take priority over acquisitions in the transfer window.
Mainz coach Thomas Tuchel has ridiculed speculation linking him with the coaching job at Bundesliga rivals Schalke, saying the reports are "disrespectful" towards current boss Huub Stevens.
Stevens' contract expires in the summer and negotiations over an extension are yet to take place.
Reports in Germany claim Tuchel is at the top of Schalke's list to replace the Dutchman, but speaking after his side's 2-0 defeat to Borussia Monchengladbach, the Mainz coach said the speculation was unnecessary.
"I cannot understand it, it's disrespectful towards Huub Stevens," he said. "It really makes you think when something like that becomes an issue. Things are being written by people who don't even have to take responsibility for their own actions.
"The ease with which such an issue can snowball is not good."
Mainz's general manager Christian Heidel has categorically ruled out a move, saying: "There is more chance that (Lionel) Messi will join Mainz than Thomas Tuchel will coach Schalke."
The two sides meet in the third round of the DFB-Pokal on December 18.