So the GM and coach are both enamored with McLeod based on comments and usage (McLoed getting a ton of key FOs and he's been used to win a FO and go off the ice a few times IRC). He's signed for 975,000 x 2 with RFA rights afterward so let's say 3.5 more years of team control, and he plays an important position (C) for a coach/GM trying to build a proper winner at some point in the next 2 years.
It would have to be a roster player, that's clearly better than McLeod to help the team win games. Devils don't really have a 4C (Boqvist) that the FO is confident in, so it would be tough to find a non C trade, in particular on Colorado. I know you are probably thinking Compher who can play C, but that's a tough sell for me. Devils could use help on D but there's not really a player in Colorado that fits.
As i'm trying to make clear, the GM and coach love the 4th line and are in love with what McLeod brings, but the problem is it's a great 4th line for a team that needs to build a top 9.
Edit: Jost as Blackjack mentioned I don't know enough about other than he's been majorly disappointing and hasn't really carved out a role like Mcleod has.