He signed the big contract, who are you trading for him?
What big contract are you talking about?
Noel refused the big contract offer from Dallas and instead signed to play this year on their Qualifying Offer, which is only 4.2M.
I assume that billysan's notion is that we could trade Marcus Morris' 5M contract for him. Per CBA trade financials, that would work. Dallas might even be interested in that.
There are some issues in the way of the notion, though.
First off, the reason Noel is playing on the QO is that it means that he will become an Unrestricted Free Agent this coming summer.
Second, again because he is playing on the QO, if Noel is traded this season, the team that gets him will not have Bird Rights. They will take two more years with that team to vest.
Third, because his Bird Rights would not transfer, Noel has right of refusal on the trade.
Now, if the Celtics were due to be well below the salary cap or had a large enough exception available next summer that they could go ahead and sign Noel without Bird Rights, then trading for him would make sense. He'd probably OK the trade (the Celtics being a team he would likely approve going to) and they would pull the trigger.
But they won't have cap room and they will only have the mid-level-exception, which is well below the level of money that Noel is looking for.
This means that if we did this trade, we would lose Noel to free agency in the summer.
Even if Noel long-term WANTS to be a Celtic, it would actually NOT be in his interest to approve such a trade (unless he's willing to play for a well-under-market deal for a couple of seasons). He'd be better served to just play out the QO and reach UFA status but with Dallas holding his Bird Rights. That would not only mean that Dallas could potentially pay him more, but it would also potentially enable them to sign & trade him to another team that might be over the cap. 'Not saying that is the most likely thing, but it simply increases his options, which is good for his market value.
Short version: Purely for technical reasons, Nerlens Noel is almost certainly not a mid-season trade option for the Celtics.