Thomas Tuchel has insisted age will have no bearing on Thiago Silva's Chelsea future.
The evergreen Brazil defender turned 37 this week and is already the second oldest active Premier League player, behind Watford goalkeeper Ben Foster.
The former Paris St Germain centre-back signed a one-year contract extension in June for a second Stamford Bridge campaign and continues to belie his advancing years through commanding performances.
And Blues boss Tuchel believes form and form alone will determine how long he can keep on extending his west London tenure.
"It's on him, it's on him; I cannot answer this question right now, but hopefully he can continue to perform on this kind of level," said Tuchel.
"And that's all it needs, to stay here. It's as easy and as clear as that. We want top performance. When you play for Chelsea you need to deliver and this is what he is doing.
"That he is a top professional is a given because otherwise it would not be possible that he plays on that kind of level for so, so many years. But age does not play a role."
Chelsea's defensive situation currently sits in a state of flux, with Cesar Azpilicueta, Andreas Christensen and Toni Rudiger's contracts expiring at the end of the campaign.
Chelsea could make another move for Sevilla's France star Jules Kounde following their rebuffed bid in the summer.
Academy product Trevoh Chalobah has also stepped impressively into the first-team squad this term to boost resources.
But Tuchel has continually offered high praise of Silva's leadership, calmness, authority and ability and sees no reason for any of that to alter any time soon.
"The only question we need to ask at the end of the season, is he still on the level that we need at Chelsea to compete for everything and every competition? Yes or no," said Tuchel.
"It's as easy as that and we have time for that. We don't need to answer that question right now. But he's in a good place and we're happy."
