Arsenal centre-back Upson, who is two months into his three month loan spell at Reading, put in a cracking performance on Saturday as the Madejski Stadium side defeated Millwall 2-0.
The 23-year-old chose Reading ahead of Millwall, snubbing Mark McGhee's offer of a loan spell with the Lions. Upson said that he considered the facilities and the potential the Royals had was greater than McGhee could offer at the New Den.
However, Lions goalkeeper Tony Warner sugeested that Upson could have made an error in his judgement as Millwall are a great club.
The former Liverpool goalkeeper, who appeared to be at fault for Reading's first goal, told thisislondon.co.uk: "I do not know much about Reading's facilities, but Millwall are a big club and we have got lots of potential.
"We have some great players, but have been unlucky with injuries this season. But we know we are not a bad side, and if we can string a few wins together we will be right back up there."
Meanwhile, former Millwall player Ricky Newman will miss Reading's clash with Sheffield United through suspension. The 32-year-old picked up his fifth booking of the season on Saturday and must now serve a one match ban.