UPDATE (12:48 P.M.): ESPN’S Chris Sheridan is reporting that the teams have a tentative agreement that will send Eddie House, Bill Walker and J.R. Giddens to New York for Nate Robinson and an unidentified second player. It’s likely that that the other player is coming from somewhere other than New York, since none of the other Knicks make the salary cap math work.

The Knicks have been engaged with the Rockets, and now the Kings, on a deal for Tracy McGrady. Keep an eye on those two teams as the afternoon progresses toward the 3 p.m. deadline.

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The Celtics want Nate Robinson. The Knicks want Eddie House. That’s the easy part.

House told reporters in Los Angeles, where the Celtics are getting ready to play the Lakers Thursday, that he expects to be traded before Thursday’s 3 p.m. deadline. Robinson also reportedly cleaned out his locker in New York and was scratched from the Knicks game against the Bulls with what the team said was the flu.

The Celtics have targeted Robinson for a month and House has a relationship with Knicks coach Mike D’Antoni going back to their days together in Phoenix. And yet, it’s still not done.

The problem, as it’s been from the start, is that Robinson’s contract status as a base year compensation player makes him difficult to trade. The Knicks won’t take back anything for Robinson other than expiring contracts and while the Celtics have many players who fit that bill, none of them make the math work in a straight-up trade.

The Celtics can’t trade House straight-up for Robinson. They can’t trade Tony Allen or Brian Scalabrine straight-up for him. Draft picks won’t help either. That leaves them with two options.

They can start to assemble a deal with multiple players involved — and reports have had everyone from J.R. Giddens to Bill Walker in the mix. Or, they can try to find a third team to bring into it who would then absorb some of the salaries. To date, no third team has been identified.

It’s also worth noting that the Knicks are at the 15-player maximum, which doesn’t leave them with a lot of wiggle room. The Celtics have had an open roster spot since the release of Lester Hudson. In other words, the Knicks can’t take back more players than they trade. (Minor update to this: The Knicks worked out a trade that sent Darko Milicic to Minnesota for Brian Cardinal and they are expected to waive Cardinal, which would free up a roster spot).

There is every reason to believe that the Celtics will wind up with Robinson in their backcourt. It’s just not clear how yet.