Robbie Savage says Ruben Dias must be considered one of Manchester City's best ever signings.
The centre-back was once again in fine form as City overcame West Ham 2-1 on Saturday, with Dias and defensive partner John Stones both finding the net.
Dias and Stones have formed a strong partnership in defence this season, with the duo having scored more than they have conceded in the 16 games they have started together.
Speaking on BT Sport, Savage says Dias' impact on his teammates since joining from Benfica in the summer means he must be considered one of City's best ever signings.
Savage also compared the 23-year-old's near-immediate impact on the side to that of Virgil van Dijk's at Liverpool.
"I think this City team have a chance of a quadruple thanks to their defensive stability," he said.
"Stones and Dias have been remarkable. You look at Liverpool's title defence, if they have a different centre-back pairing again, that will be 19 different partnerships at the back, which impacts the whole team.
"The stability Man City have got now with that defensive unit and their attacking threat, that, for me, is why they're on form."
He added: "I think Dias' impact is as good as, if not better than, Van Dijk's instant impact on Liverpool.
Manchester City consolidated their position at the top of the league with a 1-0 win over Arsenal on Sunday.
Is the title all theirs already?
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"The way he's made players better around him, look at the full-backs and Cancello's form.
"Pep's evolved this side, they were 14th in November and then he changed a little bit with Cancelo going inside in a free role.
"For me, Dias has to be up there with one of the best signings City have ever made."