With three wins from three, England top Pool D ahead of their trip to Lille this weekend having beaten Argentina, Japan and Chile.
The 2003 World Cup winners are expected to face Fiji or Wales in the knock-out stages on the weekend of October 14th-15th in Marseille. Those two sides from Pool C also play over the coming days.
"It's only about Saturday and Samoa," Sinfield told reporters.
"We'll worry about what is to come Saturday evening when our game is over.
"There's still a bit that we have to wait for in that group so it would be foolish for us to spend our whole time on that when we don't quite know."
Despite struggling to fire in attack, England's defence has been very promising during the tournament.
They have conceded one try and just 22 points, the fewest of all 20 teams in the competition so far.
"We try to make it important," Sinfield said of playing without the ball.
"Typically the best defensive team of any competition wins the competition or league or cup."
"We all understand that," the former England rugby league international added.
Curry 'jinx'
Flanker Tom Curry is set to return from a ban to face the Pacific Islanders in northern France after being sent off early into England's opening World Cup game against Argentina.
"I talked him up a bit too much last time and we ended up with two minutes from him, I'm not going to spend as much time on him today," Sinfield joked.
"He's a world class player. We hope to see him for a bit longer this week.
"With the way he goes around his business, how hard he trains, it's great to have him available."
Another selection dilemma for Sinfield and his head coach Steve Borthwick, who name their side on Thursday, will be at fly-half.
Captain Owen Farrell returned from a ban of his own in the victory over Chile after George Ford and his goal-kicking steered England past Argentina and Japan.
Marcus Smith is also another playmaking option as is having all three on the field with Ford in the No. 10 shirt, Farrell at centre and Smith as a full-back.
"Whoever you throw the ball to they're probably going to make a good decision off the back of what you give them," scrum-half Danny Care said.
"They're always talking, wanting the ball, commentating. We're very lucky to have all there.
"The connections they can bring together is pretty unique. We've shown glimpses and hopefully we can keep showing more of that."
