Thornton and Marleau both own no-movement clauses and would have to approve any deal the Sharks attempt to complete.
One league source told TFP that as of Sunday night, the Sharks have not approached Thornton about waiving his no-movement clause, nor have they broached the subject, other than to indicate the team plans on getting younger and building around Logan Couture, Joe Pavelski and Marc-Edouard Vlasic.
A separate source confirmed that the Sharks met with Marleau on Friday, though it's unknown if the team discussed the possibility of an off-season trade.
Pagnotta indicates that while it is unlikely Thornton would waive his no-movement clause this off-season, he would consider it under "extenuating circumstances."
Thornton, 34, signed a three-year, $20.25 million contract extension on Jan. 24, while Marleau, 34, signed a three-year, $20 million extension that same day. Both deals kick in July 1.
Niemi, 30, will enter the final-year of his four-year, $15.2 million contract next season. While his salary cap hit is $3.8 million, he's owed $4 million in actual salary. He does not own a no-trade or no-movement clause.
While trading Thornton or Marleau is not a guarantee and may prove to be difficult, given their no-movement clauses and desire to both stay in San Jose, Pagnotta is also reporting the Sharks' preference to get younger in goal.
Sharks GM Doug Wilson is trying to re-sign netminder Alex Stalock and hopes to acquire a young goalie this off-season, which could come as part of a package for Marleau or Thornton, or through another deal, perhaps involving Niemi.
Several teams, including the Sharks, are expected to make significant roster changes this off-season.
The Ottawa Senators are expected to trade captain Jason Spezza, as first reported by Pagnotta on Mar. 3; the Toronto Maple Leafs are reportedly looking to shake up their roster and are taking calls on captain Dion Phaneuf, among others; the Winnipeg Jets will continue to consider deals for star left wing Evander Kane; and the Vancouver Canucks, once a new GM is hired, must decide whether or not to trade the likes of Ryan Kesler and Alexander Edler, both of whom were almost dealt prior to the Mar. 5 trade deadline.
Thornton has been among the League leaders in points for the majority of his career and the asking price will presumably be steep.
In 82 games with the Sharks this season, Thornton registered 11 goals and 76 points. His 65 assists placed him second in the NHL in that category only to Pittsburgh Penguins captain Sidney Crosby.
Marleau also played 82 games with the Sharks this year, picking up 33 goals and 37 assists for 70 points.
The Sharks have already started tinkering with their roster. As they announced on Thursday, they will not bring back defenseman Dan Boyle and right wing Martin Havlat next season.
Boyle will become an unrestricted free agent July 1, while Havlat, who has one-year left on his contract, will be bought out unless the Sharks can trade him.
Trade talks are expected to pick up in the coming weeks and could intensify closer to the NHL Draft on June 27-28 in Philadelphia.
TFP Editor-in-Chief David Pagnotta contributed to this report.