Ahead of Monday's clash with Portsmouth, Charlton have suffered a severe blow with the news that Miles Leaburn will not be available for several weeks after suffering ankle ligament damage: https://londonnewsonline.co.uk/charlton-athletic-get-bad-news-on-miles-leaburns-injury-top-scorer-facing-a-prolonged-spell-on-the-sidelines/
After yesterday's results, Charlton are back to 14th in the table and they are only that high because of goal difference. There are five clubs on 16 points and the relegation zone is only four points away.
Ben Garner admits that Portsmouth did really well in the transfer window: https://www.portsmouth.co.uk/sport/football/portsmouth-fc/charlton-boss-reveals-whats-impressed-him-most-about-portsmouth-this-season-and-confirms-huge-injury-blow-ahead-of-valley-clash-3881540
I am going from memory on this, but I think we have played Portsmouth more than any other team in league matches, reflecting the fact that we have often been in the same division.