Thomas Tuchel has told Andreas Christensen it is time to "walk the talk" by committing his future to Chelsea following protracted contract discussions.
Blues boss Tuchel was expecting imminent good news on the defender's future almost two weeks ago.
But Denmark international Christensen, whose existing deal expires at the end of the season, has seemingly stalled on putting pen to paper.
The 25-year-old was an unused substitute for the club's last three fixtures and, ahead of Wednesday's trip to Watford, may remain on the bench until the matter is resolved.
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"We have to hope that it influences the contract situation a little bit," Tuchel said of Christensen's lack of action in recent weeks.
"My understanding was that it was a matter of a very short period before we had good news.
"As I understood it, the club wants the same, the player wants the same, the coach wants the same: to stay.
"And that's why for me it was a zero-problem situation.
"But we are waiting a long time now for confirmation and it's on Andreas to act. How he acts on the pitch, he needs to act now off the pitch and walk the talk because he tells us that he loves Chelsea.
"He tells us that he wants to stay. He is a big part of a big club and I think he is a perfect fit and I think his career here is by far not finished.
"But, like I said, it's on him. We want the commitment and hopefully we get it."
Premier League leaders Chelsea head to Vicarage Road a point clear of champions Manchester City following Sunday's frustrating 1-1 draw with Manchester United.
Tuchel was boosted by Romelu Lukaku's return from an ankle problem against United.
The German believes the late cameo will give his £97.5m record signing a mental lift following more than a month out and has "zero doubts" the striker will be a major success during his second spell at Stamford Bridge.
"The most important thing for me is that he becomes fit and gains a physical level that he can start for us and the rest, I'm pretty sure, will take care of itself because Romelu is a winner, is a champion and is hungry for more," said Tuchel.
"I am absolutely convinced, I have zero doubts, that he will have a huge impact into our team.
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"We gave him now some minutes, I think that helps him psychologically and this is very important. But he is happy, he smiles every day, he's determined, he trains on a very high level.
"We still believe that he can make the difference for us. Tomorrow he is with the team and he has a big chance to play.
"But at the same time we will still be patient."
Chelsea trio Reece James, Jorginho and Timo Werner face late fitness tests, while injured trio Ben Chilwell, N'Golo Kante and Mateo Kovacic will be absent against Watford.
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