"But you never know. That's why I have to be very careful."
If Federer gets past Soderling, awaiting him will be Ivo Karlovic, who has served 102 aces in his three matches so far, or Spain's seventh seed Fernando Verdasco.
Federer's possible semi-final opponent is fourth seed Novak Djokovic, who is up against Israeli surprise package Dudi Sela on Monday.
The Serb has barely merited a mention as a title contender, but he says he is happy for it to stay that way.
"Andy Murray and Roger Federer are in the spotlight, and obviously they deserve to be in that situation because they have been playing great tennis the last six, seven months," he said after cruising past Mardy Fish in the last round.
"But you have to look from the brighter side. I think it's good. It releases the pressure for me."
Venus had few problems in reaching the fourth round
In the women's draw, Venus Williams will continue her bid for a sixth Wimbledon title when she takes on Ana Ivanovic. They are first on Court One at 1300.
Ivanovic, the former world number one, has shown signs of a resurgence after losing her way over the last year, but Venus will nonetheless be a strong favourite.
"I'm very excited," said former world number one Ivanovic.
"She's a very dangerous opponent, but I think I have a great chance, and I feel very comfortable going in that match. I'm so excited to have opportunity for that challenge."
Venus's sister Serena is up against Daniela Hantuchova - who is looking to reach the quarter-finals for the first time since 2002 - second on Court Two.
"She's such a smooth player," said Serena of her unseeded Slovakian opponent.
"I have to make sure I don't rush myself because she is playing well and I think she's moving well. So I'm going to have to really bring a tough game."
Second on Centre Court, top seed Dinara Safina will meet 2006 champion Amelie Mauresmo in her first fourth-round appearance at Wimbledon.
"She's playing very good. I think she's back in her best shape," said the Russian.
"She likes playing on grass. I mean, she won Wimbledon. So I think it's going to be not an easy match. So I'm looking forward. I just want to focus on myself, play my game."
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