“You’re always looking for a No. 6, a No. 7, and a No. 8,’’ Red Sox general manager Theo Epstein said earlier his month. “You can’t have enough depth.’’

So while the Sox have holes in left field and at shortstop, Epstein will spend much of the coming weeks identifying and pursuing starting pitchers who can fill in when the inevitable need arises.

As it stands, the Sox have a rotation of Jon Lester, Josh Beckett, Daisuke Matsuzaka, Clay Buchholz, and Tim Wakefield in place for next season.

But Buchholz has yet to throw more than 92 innings in a major league season and has a career ERA of 4.91. The coming season is expected to be a strong one for Buchholz, 25, given the progress he showed in August and September - that is, unless he becomes the centerpiece in a trade for an established star such as Toronto ace Roy Halladay.

The 43-year-old Wakefield made only four starts after July 8 and was not on the postseason roster because of a back injury that required surgery after the season. The hope is that Wake field will be ready for the start of the season, but Epstein already has acknowledged that it’s unrealistic to expect the knuckleballer to make 30 starts given his age and the back injury.

The only prospect close to major league proficiency is 24-year-old righthander Junichi Tazawa, who made four starts for the Sox last season after going 9-7 with a 2.55 ERA in the minor leagues.

Epstein tried filling the gaps last season with three veteran pitchers, signing Brad Penny and John Smoltz before the season, then Paul Byrd in August. The trio was 10-16 with a 6.17 ERA; the Sox went 16-22 in the games they started. They did give the Sox 205 2/3 innings, though.

Smoltz and Penny were released in August, having cost the Sox approximately $8 million.

Given their other needs, the Sox are unlikely to pursue John Lackey, Randy Wolf, or any of the other notable starters on the free agent market. But they figure to be active with the second and third tier of available starters.

Ben Sheets could be the prize pickup in that group. The 31-year-old righthander has not pitched in 14 months because of a torn flexor tendon. Sheets had surgery in February and skipped the entire 2009 season to rehab, working at TMI Sports Medicine in Arlington, Texas.

“He is recovering well and will be 100 percent by spring training,’’ agent Casey Close wrote in an e-mail.

As a Milwaukee Brewer, Sheets started the 2008 All-Star Game at Yankee Stadium for the National League, throwing two scoreless innings. He is 25-14 with a 3.39 in his last two seasons.

Because of his injury history, Sheets is expected to throw for interested teams at some point in the next month.

Righthander Rich Harden is a similar pitcher, having not thrown more than 148 innings since the 2004 season. He was 9-9 with an unimpressive 4.09 ERA for the Cubs last season and was shut down at the end of the season with assorted aches.

But he has a 3.05 ERA over the last two seasons and 29 more strikeouts than innings pitched in his career. Harden also spent six seasons in Oakland, giving him the American League experience that Penny and Smoltz did not have. The combination of a depressed market and his lack of durability could make Harden an affordable pickup.

“He’s ready to pitch,’’ agent Arn Tellem said. “If the Cubs were in contention, he would have been pitching at the end of the season. There are no restrictions.’’

Erik Bedard, the one-time ace of the Baltimore Orioles, is on the market after a disastrous two-year tenure with the Seattle Mariners in which he started only 30 games. But Bedard had a 3.24 ERA in those games. He had shoulder surgery in August.

Justin Duchscherer, a two-time All-Star for Oakland, missed all of 2009 recovering from elbow surgery that was compounded by depression.

If the Yankees do not tender a contract to Chien-Ming Wang, the sinkerball specialist could intrigue the Red Sox. Wang was 54-20 with a 3.79 ERA before a foot injury midway through the 2008 season derailed his career. Only 29, Wang is coming off shoulder surgery and is expected to be ready by May or June.

Wang has said he would like to remain in the American League if he becomes a free agent. He was 1-6 with a 9.64 ERA last season.

Other pitchers coming back from injuries include Kelvim Escobar, Mark Mulder (who is expected to join pitching coach Rick Peterson in Milwaukee), Mark Prior, and Noah Lowry.

“There are a lot of rocks you can turn over,’’ said Yankees general manager Brian Cashman, who last season gave starts to Sergio Mitre and Chad Gaudin. “Every GM in the game is looking for pitchers they can plug into their rotations when there is a need.’’

Peter Abraham can be reached at pabraham@globe.com.