The first week of NFL free agency was almost too much for even Twitter to handle. Players were being signed, waived or traded almost faster than fingers could type the news – even in just 140 characters.

And after all those early moves, this much is certain: The Super Bowl champion New England Patriots have some work to do.

Five players who played pivotal roles in New England’s championship have signed to play elsewhere, led by cornerbacks Darrelle Revis (New York Jets) and Brandon Browner (New Orleans Saints), and running back Shane Vereen (New York Giants). Several others have been released and not signed elsewhere yet, including defensive tackle Vince Wilfork, running back Stevan Ridley and offensive lineman Dan Connolly.

Those subtractions have prompted Patriots fans to swallow hard. Even with the free agents the Patriots have signed in recent days, this team is weaker today than it was a week ago. And every one of New England’s AFC East foes – the Jets, Miami Dolphins and Buffalo Bills – have gotten better, closing the gap.

So what’s next for Bill Belichick and others?

Let’s start with rebuilding the defense, focusing more on the front seven than the secondary.

Revis cannot be replaced. There’s no free agent out there, and certainly no player available in the draft, who’s going to step in and shut down half the field like he could. And once Revis left, there was no way the Patriots were going to keep Browner. The two excelled at playing press man-to-man defense, allowing the safeties to provide coverage over the deep part of the field. Yes, the Patriots kept one of their defensive leaders (which was vital with Wilfork’s release) by re-signing safety Devin McCourty to big money. There are also some decent cornerbacks on the roster, such as Kyle Arrington, Logan Ryan and Alfonzo Dennard. And, of course, there’s Super Bowl hero Malcolm Butler, whose goal-line interception was the difference between a fourth Vince Lombardi trophy and a third last-second loss.

But none of them, including Chimdi Chekwa, the former Oakland Raiders cornerback signed by New England last week, or any of the available free agents can play man-to-man defense like Revis and Browner. So look for the Patriots to return to playing mostly zone defense in the secondary and revert to their past bend-but-don’t-break defensive style, giving up a lot of yards but buckling down in the red zone to limit the scoring.

And if the Patriots are playing zone defense, they’ll need a better pass rush. New England had 40 sacks in the regular season and three in the playoffs, all coming in its 28-24 Super Bowl victory over Seattle. The 40 sacks tied for 13th-best in the NFL. That’s not bad, but mostly it’s a reflection of how the team relied on its excellent secondary to shut down quarterbacks.

The Patriots have some pieces in place, with defensive ends Chandler Jones and Rob Ninkovich, and defensive tackle Dominique Easley, their No. 1 pick last year. And they signed former Cleveland defensive end/linebacker Jabaal Sheard, a 2011 second-round pick who can play inside or outside on the defensive line. He had 23 sacks and seven forced fumbles in his four years with the Browns. New England looks at the 6-foot-3, 265-pound Sheard as someone who can help stuff the run and rush the passer.

They also need to find a big man in the middle of the defensive line. Anyone who ever played behind Wilfork spoke about how easy he made it for them. Wilfork would command a double team on almost every running play, leaving a linebacker free to take on the running back. Wilfork could return to the Patriots, though that’s doubtful. Most folks think he’ll end up in Houston, with Coach Bill O’Brien and defensive coordinator Romeo Crennel (former Patriots coaches), or Indianapolis, where former University of Miami teammates Frank Gore and Andre Johnson are trying to recruit him.

Sealver Silega has the size (6-2, 325) to replace him, but played his best with Wilfork next to him. And Easley could take his spot, but isn’t the same type of run stuffer that Wilfork was. It’s also possible the Patriots could go after free agents Randy Starks and Red Bryant.

Linebacker Jerod Mayo’s return will help the run defense. But he hasn’t played a full season since 2012, so there’s a significant injury risk.

The defense is going to be built around guys like Jones and McCourty, and linebackers Dont’a Hightower and Jamie Collins. And while that’s a good start, they need help.

Offensively, the Patriots need to address their third-down back with Vereen gone, and the offensive line, with Connolly possibly gone.

Connolly was a team captain last year and well-liked in the locker room. If he leaves, the Patriots likely will look to draft his replacement.

Trade rumors have New England interested in Philadelphia guard Evan Mathis, a Pro Bowler each of the last two seasons. He would be a good fit, though he was limited to nine games last year because of a knee injury.

The big question mark is in the backfield, where Vereen has left and Ridley is also a free agent.

The Patriots have some options on their roster: LeGarrette Blount, Jonas Gray, Brandon Bolden, James White and a sleeper in rookie Tyler Gaffney. New England claimed Gaffney off waivers last July after he suffered a season-ending knee injury in Carolina’s training camp. He spent the year on injured reserve, learning the Patriots’ game from the veterans as he rehabbed.

While at Stanford in 2013, Gaffney rushed for 1,709 yards and 21 touchdowns. He could be a surprise next season.

But New England still wants that third-down back who can create matchup problems for a defense. They brought in Reggie Bush for a visit Friday, but the dynamic second pick of the 2006 draft – who was let go by the Detroit Lions after an injury-filled season – signed with San Francisco on Saturday. He rushed for more than 1,000 yards in 2013 with Detroit and only 297 last season.

So there is a significant hole that still needs filling on the offensive side of the ball.

New England took a big step to giving Tom Brady more threats by reportedly signing former Buffalo tight end Scott Chandler, who had some of his best games against the Patriots. He is a talented receiver and could combine with Rob Gronkowski to give the Patriots two huge targets.

The Patriots signed a couple of receivers last week – Kevin Dorsey of Green Bay and Brandon Gibson of Miami – and re-signed Brian Tyms, who didn’t play much last season but may be the best deep threat on the roster. Or that might be Josh Boyce, a third-year player who spent last year mostly on the practice squad.

Whatever happens in the days ahead, you can be sure the Patriots and Belichick won’t sit still. There’s a long way to go to September … and beyond.