Red Sox know they have to fix their pitching staff, but how will they go about it?

Japanese free agent Kodai Senga could be on the Red Sox' radar as they look to strengthen their rotation.Matt Slocum/Associated Press

As much as the start of the offseason has been dominated by questions about the future of Xander Bogaerts, it’s far from the only issue confronting the Red Sox.

They had a 4.53 ERA last season, sixth worst in MLB. None of the 12 playoff teams had a mark worse than 3.97. How important is it for the Sox to upgrade their staff?

“It’s huge,” said chief baseball officer Chaim Bloom. “Some of that solution will come from within and getting the guys that we have, who we like, to better their performance, but we’re definitely looking to add pitching from the outside.”

Does that mean a specific caliber of pitcher — a front-of-the-rotation starter (Justin Verlander, Jacob deGrom, Carlos Rodón), a mid-rotation starter (Nate Eovaldi, Japanese free agent Kodai Senga, Chris Bassitt, Michael Wacha), or an established late-inning reliever (Kenley Jansen, Taylor Rogers)? Maybe a trade for pitching help?

“I wouldn’t rule anybody out,” said Bloom.

But according to multiple sources, the Sox seem unlikely to shop at the top of the starter market (Verlander, deGrom, and Rodón, or Bassitt, who received a qualifying offer from the Mets) at least at this stage of the offseason, with Bogaerts remaining atop their priority list.

On paper, the Sox have Chris Sale, Nick Pivetta, Brayan Bello, Garrett Whitlock, James Paxton, Tanner Houck, and Kutter Crawford. Behind them, they believe next year’s Triple A rotation candidates — including righties Bryan Mata and Josh Winckowski and lefties Brandon Walter and Chris Murphy — eventually could yield another homegrown starter or two.

Still, that group is not enough. The starters had a 4.49 ERA last year. Even with an expectation that Sale and Paxton will contribute more than two combined starts, the Sox are currently without the 69 combined made by free agents Rich Hill (26), Wacha (23), and Eovaldi (20).

“We’re looking to add starting pitching to continue to build depth and continue to add to the rotation,” general manager Brian O’Halloran said. “We’re just looking to build a really good rotation — a championship-caliber rotation. We have some depth and certainly some quality and we want to add more.”

Questions about the current group abound. The Sox believe Whitlock (35.6 percent strikeout rate in the season’s first month, split between the rotation and bullpen) has mid-rotation upside, but he has thrown more than 85 innings just once in his professional career (2018). For all of his promise down the stretch (3.12 ERA, one homer, and a ton of grounders in his last eight starts), Bello has never pitched a full, injury-free six-month season in a rotation.

Nick Pivetta had a career-high 33 starts for the Red Sox in 2022.Jim Davis/Globe Staff

Though Paxton and Sale are expected to be healthy for spring training, they’ve thrown fewer than 70 innings combined since the start of 2020. What’s a reasonable projection for combined starts? Twenty? Forty?

Pivetta (10-12, 4.56) was the lone durable presence in 2022, and there’s value in that. Still, his dire struggles against the AL East (1-8, 6.72 in 16 starts) raise concerns about his future in a division whose hitters are very familiar with his arsenal.

The Sox would like to bring back Eovaldi — who rejected a one-year, $19.65 million deal — on a multiyear pact. If not, Senga may be the most interesting target who would (a) fit into the Eovaldi-ish budget slot and (b) not cost draft picks.

Other names who might fit on short-term deals include lefthander Andrew Heaney (35.0 percent strikeout rate in 2022, third highest among starters who threw 50 innings) or veterans such as Hill, Wacha, and Corey Kluber.

The need to upgrade the bullpen may be even more acute. Sox relievers had a 4.59 ERA, fifth worst in MLB. The returning trio of John Schreiber, Matt Barnes (who rebounded down the stretch after a brutal beginning), and Houck gives the Sox late-innings options.

But they are without two of their better relievers from a year ago. Whitlock is penciled into the rotation and lefty Matt Strahm is a free agent.

Garrett Whitlock was used as a reliever last season, but the Red Sox believe he has mod-rotation potential.Barry Chin/Globe Staff

“We want to add. We know we need to improve,” O’Halloran said of the bullpen. “Who ends up being the closer, it’s way too early to say now whether that’s someone who’s here now or that’s someone that we acquire. But we’re looking to build a championship-caliber bullpen.”

Under Bloom, the Sox’ biggest outlay for a free agent reliever has been a two-year, $8 million deal for lefty Jake Diekman, who was traded at the deadline. Last year, the Sox also made a two-year offer in the same ballpark for lefty Brooks Raley, but were outbid by the Rays. They came to regret not pursuing relief help more aggressively.

Yet according to major league sources, the Sox to this point have focused more on Bogaerts and Eovaldi as well as the starting pitching market than on the bullpen. Meanwhile, the reliever market has already taken a shock, with five-year deals for Mets closer Edwin Díaz ($102 million) and Padres setup man Robert Suarez ($46 million), and a three-year, $31.5 million extension for Rafael Montero.

Where do those early signings point the Red Sox? Do they make it more likely that the team will redirect to the trade market?

It’s still too early to say, save for the fact that the Sox recognize their efforts to recover from a last-place campaign will rely in no small part on adding to the pitching staff, likely with acquisitions of a sort they have not previously made under Bloom.