The Lightning made a big splash Thursday, addressing its biggest long-term need by acquiring potential top-pairing defenseman Mikhail Sergachev in the Jonathan Drouin trade to Montreal.This move, however, was as much about the future as the present. There's no guarantee Sergachev, 18, starts next season in Tampa Bay, but he's setting up Tampa Bay for years to come with a very valuable piece (at a cap-friendly price).And keep this in mind: GM Steve Yzerman doesn't sound like he's done shopping for a defenseman who could have an immediate impact. There could even be some more action by Saturday's 2 p.m. roster freeze, which runs through Wednesday's expansion draft in Las Vegas. There are many established defensemen that be available this weekend, teams with protection list issues not wanting to lose them to expansion Vegas for nothing.Yzerman said Thursday's deal for Sergachev doesn't preclude him from acquiring another defenseman. The Lightning may not have top trade chip in Drouin, but still has depth at forward, and a strong prospect pool to work with. And Tampa Bay has some more cap flexibility, too."We'll look at anything," Yzerman said. "(Sergachev) doesn't take me out of trying to acquire another defenseman. If another defenseman is out there and a fit and makes us better, we'd look at it for sure."Who could the Lightning target? You can start with teams who need to move a defenseman before the expansion draft. Matt Dumba/Jonas Brodin, Wild The Wild reportedly was hot after Drouin, too. While that Lightning trade chip is gone, Minnesota's glut on defense is not. GM Cliff Fletcher told the Minneapolis Star Tribune that he's "definitely actively listening" and has received "quality trade offers" on defensemen Jonas Brodin and Matt Dumba. Dumba, 22, is a right-shot defenseman who has just one year left on his contract (at an affordable $2.55 million) before becoming a restricted free agent next summer. Brodin, 23, a left-shot, is under contract through 2020-21 with an annual cap hit of $4.16 million.Minnesota is likely looking for a forward in return, and there will be no shortage of suitors, especially for Brodin. Associated Press Matt Dumba has just one year left on his contract before becoming a restricted free agent next summer. Associated Press Jonas Brodin, who likely will have plenty of suitors, is under contract through 2020-21. Associated Press Matt Dumba has just one year left on his contract before becoming a restricted free agent next summer. Associated Press Jonas Brodin, who likely will have plenty of suitors, is under contract through 2020-21. Sami Vatanen, Ducks Vatanen is likely going to be squeezed out by the Ducks due to its depth on the blueline, and will be out four to five months following shoulder surgery. But he's still a solid option as a right-shot defenseman, a 26-year old who carries a $4.875 million cap hit through 2019-20. The injury hasn't stopped teams from being interested in Vatanen, who could also be pursued by the likes of the Devils and Maple Leafs.Whether the Lightning would have the necessary pieces remains to be seen, but prospects could be helpful since they won't have to be exposed in the expansion draft. Associated Press Shoulder surgery hasn't diminished other teams' interest in Anaiem's Sami Vatanen. Associated Press Shoulder surgery hasn't diminished other teams' interest in Anaiem's Sami Vatanen. Travis Hamonic/Calvin de Haan, Islanders Another right-shot defenseman, Hamonic also boasts some size, at 6-2, 205 pounds, an alternate captain with the Islanders. He carries a $3.85 million cap hit through 2019-20. He's coming off a rough season (14 points, minus-21), but Calvin de Haan had his best one (25 points, plus-15). Both could be second-pair caliber defensemen. De Haan is an RFA this summer.The Islanders are also likely looking for some scoring punch.There could even be other defensemen who are available — who saw the Sergachev return coming? But the point is, Yzerman's busy summer has only begun. Getty Images The Islanders' Calvin de Haan has mixed it up with Lightning players in the past. Douglas R. Clifford | Times Travis Hamonic, an alternate captain with the Islanders, didn't have his best season recently. Getty Images The Islanders' Calvin de Haan has mixed it up with Lightning players in the past. Douglas R. Clifford | Times Travis Hamonic, an alternate captain with the Islanders, didn't have his best season recently. Joe Smith can be reached at firstname.lastname@example.org. Follow @TBTimes_JSmith.