"This is a massive game," Sidwell told the Royals' official website, www.readingfc.co.uk.
"When we played them earlier in the season, we had a funny spell, results hadn't gone for us, but then we beat them and this could be the one that sets us on a run again.
"They've done really well, they've got a very good home record and it's a tough place to go.
"They're banging goals in but, if we go there with the winning mindset, hopefully we can come away with something."
Sidwell believes Dimitar Berbatov will provide Spurs' main threat, with the Bulgarian marksman having fired 19 goals already this season.
"Berbatov has been fantstic for them, he's come into his own and he's playing with confidence - the whole team are," Sidwell said.
"They're a well-balanced side and they're playing as a unit. At the beginning of the season, they had a lot of individuals but it's all coming together now."
Reading boss Steve Coppell signed a new two-year contract on Monday and Sidwell, whose current deal expires at the end of the season, admits his manager's decision will influence his own thinking.
"It makes a difference, of course it does," he said.
"It's fantastic and everything is key in terms of the situation with the club, where we finish in the league, what the chairman is doing and so on.
"It's great news that Steve has signed, he deserves it too. I'm sure he's happy, but you know what he's like - he won't show it."