BOSTON — The deal is not yet done, but the Rangers and Marc Staal are making progress toward a contract extension that would keep the alternate captain in New York for the next six years, The Post has learned.

A well-placed source said there had been “a productive meeting” here on Wednesday between assistant general manager Jeff Gorton and Staal’s representative, Paul Krepelka.

It is believed the sides are discussing a six-year deal between $5.6 million and $5.9 million per season for the 28-year-old defenseman, who is in his eighth season as a Ranger after having been selected 14th overall in the 2005 Entry Draft.

Staal, Martin St. Louis, Mats Zuccarello, Lee Stempniak and Matt Hunwick currently are pending unrestricted free agents while Derek Stepan, Carl Hagelin, Jesper Fast and John Moore are pending restricted free agents.

The Blueshirts appear to have approximately $20 million of available cap space for 2015-16, depending upon exactly where the cap is set for next season.

Hence, there are difficult decisions looming, but keeping Staal — who has been outstanding over the last six weeks and is an invaluable member of the blue-line core (and corps) — under contract isn’t one of the tough calls.

There is a first time for everything.

For the first time in his career that began in 2005-06, Henrik Lundqvist was a healthy backup for a game against the Bruins.

Cam Talbot was in nets for Thursday’s 3-0 defeat by the Bruins that opened a challenging road swing for the Blueshirts of three games in 3½ days that continues in Columbus on Friday and concludes in Pittsburgh on Sunday.

Lundqvist had started 30 straight regular-season games plus five in the 2013 playoffs against the Bruins. Indeed, he had started 33 of the 34 games the Rangers had played against Boston since he joined the NHL, missing just the April 8, 2006, match in Boston that Kevin Weekes won 4-3 in overtime.

Lundqvist then was ailing with a groin issue that developed after he had won a gold medal for Sweden at the Turin Olympics and forced him to miss seven straight games before starting the season finale.

There are no physical issues now. Indeed, Lundqvist worked hard on the ice Thursday morning in a session that included Moore, a healthy scratch, and goaltending coach Benoit Allaire.

Coach Alain Vigneault revealed that the schedule was determinative in his decision to go with Talbot in Boston and Lundqvist in Columbus as lead-ins to the match in Pittsburgh.

“To be truthful, we’re playing Friday and then Sunday afternoon without practicing or skating in between and I didn’t think it would be fair for the goaltender [in Boston] to then play in Pittsburgh,” he said.

Tanner Glass, in the lineup for the first time since Dec. 29 and six straight healthy scratches, fought Adam McQuaid at 7:52 of the second period.

It marked the Blueshirts’ first fight in 12 games, since Dec. 16 in Calgary when Glass fought Lance Bouma. Chris Kreider then fought Chris Kelly at 6:13 of the third when the Bruin came to teammate Carl Soderberg’s defense after he had been boarded by the Blueshirts winger.

Matt Hunwick replaced Moore as the sixth defenseman after sitting out the previous four games.