Dustin Penner, with Anaheim in December, will join the Capitals this week after he was acquired in a trade with the Ducks. (Toni L. Sandys/The Washington Post)

With the NHL’s trade deadline at 3 p.m. Wednesday, the Washington Capitals find themselves among the many teams on the playoff bubble, trying to walk the line between buyer and seller to boost their postseason hopes at a cost they can stomach.

The Capitals made one low-risk buy Tuesday afternoon, acquiring hulking left wing Dustin Penner from the Anaheim Ducks for a fourth-round pick in June’s draft. Then, Tuesday evening, Washington parted ways with disgruntled veteran Martin Erat, sending him to Phoenix with prospect John Mitchell for veteran defenseman Rostislav Klesla, prospect Chris Brown and a fourth-round draft pick in 2015.

“I don’t think any manager’s ever completely comfortable with his team. There’s always something you think you can do to make them better,” Capitals General Manager George McPhee said last week. “The issue comes down at the deadline [to] what does it cost you? Can you do it? Is it possible? Or do you like what you have, and the price of extortion makes you pass.”

Penner, 31, is a 6-foot-4, 247-pound two-time Stanley Cup winner who could slot in nicely on the Capitals’ top line with Alex Ovechkin and Nicklas Backstrom. But he’s also set to become an unrestricted free agent July 1, and his addition didn’t address Washington’s primary need of top-four defensive depth.

It’s unclear if Klesla, 31, a left-handed defenseman playing in his 13th NHL season, will fill that void. Klesla, who is also set to become an unrestricted free agent this summer, served primarily a third-pairing role in Phoenix where he fell out of favor this year. The Coyotes, who visit Washington on Saturday, even waived Klesla back in November but he went unclaimed.

Both Klesla and Brown, a 23-year-old second-round pick in 2009 who is signed through 2014-15, will initially report to the American Hockey League’s Hershey Bears. Even with Klesla in Hershey, all but $925,000 of his $2.975 million salary cap hit will count against the Capitals’ financial picture.

The Capitals have long needed an experienced, steady presence on the blue line to complement their cadre of offensive-minded defensemen, and the deficiency has been exacerbated by injuries this season. Thirteen defensemen, including seven who had played fewer than 100 NHL games entering this year, have dressed in at least one game for Washington over the first 62 games.

Klesla adds more depth, while allowing Washington to move Erat and his contract that carries another year at a $4.5 million salary cap hit. McPhee acknowledged previously that with so many teams tight against the salary cap, moving Erat when he initially requested a trade in November was difficult.

“It’s been a difficult year with transactions,” McPhee said. “Had this been a typical year we might have been able to move him within weeks of his request, but that wasn’t the case this year.”

In determining where Klesla fits, it’s worth noting he is averaging a career-low 15 minutes 31 seconds in ice time. The Capitals aren’t short of bottom-pairing defensemen, but rather those who can perform consistently in a top-four role. If Klesla isn’t able to handle those responsibilities, the alternatives are dwindling.

Two of the more appealing rest-of-season rentals were dealt elsewhere Tuesday as Mike Weaver went from Florida to Montreal and Andrew MacDonald went from the Islanders to the Flyers.

Other pending unrestricted free agents rumored to be on the block are Ottawa’s Chris Phillips and Winnipeg’s Mark Stuart. Buffalo’s Christian Ehrhoff is believed to be available, but his remaining seven years at $4 million annually would be a significant commitment. Another intriguing possibility could be Vancouver’s well-rounded Alexander Edler, who is under contract for the next five seasons with an annual salary cap hit of $5 million.

But to land someone that isn’t simply a year-end rental would take a mix of assets in the form of current players, prospects and perhaps draft picks as well. Recently, though, McPhee hasn’t often made moves for players with years left on their contract.

Of the 10 players McPhee has acquired at the trade deadline over the past six years, dating from 2007-08 when the Capitals began qualifying for the playoffs consistently, only two — Dennis Wideman and Erat — had years remaining on their contract when acquired. Only Wideman, Erat and Sergei Fedorov went on to spend the season following their trade in Washington.

Even though the deal to acquire Erat backfired, McPhee stated that he wouldn’t hesitate to help the current squad if the price was right.

“Sometimes a trade doesn’t go your way. I’m never going to bat 1,000, but I will always continue to try and help the club that’s on the ice,” McPhee said. “If there’s something at the deadline that we think is going to help this club that’s been battling all year, then we’re going to do it. I will trade picks and young players again to make this team better if that’s what is necessary.”

Capitals notes: Left wing Nicolas Deschamps was reassigned to the AHL’s Hershey Bears.