The ever-popular right-back was covering left-back for Chelsea when he went down clutching his knee.
He was substituted and a club source confirmed a medial knee ligament injury.
This could result in surgery, but he will be sidelined for a month at least.
It's a bad time for Paulo to be injured as he is a first choice for Avran Grant's side.
He is ahead of Juliano Belletti for the right back spot and was only playing left back as Ashley Cole is out injured and Wayne Bridge was suspended.
Bridge is free from his ban and will play at left back against Wigan tomorrow.
Belletti will continue at right back.