This is something that was posted before by another user yet I started investigating this a bit further with interesting results. At first I thought this would just mean playing one on one in online mode like all Fight Night games have done in the best, but if you visit the Xbox.com FNRD4 profile you will see different:

http://www.xbox.com/en-US/games/f/fightnightround4

As you can see, the orange bullets on the right (those are the online components) list Players 2 as well as Players Co-Op 1-2....so that's two different modes in there. Players 2 would mean regular online fights yet what do they mean by Players Co-Op 1-2? Is there an online trainer mode in there? Spectator mode? Or just perhaps an error on their part?

If you compare this to a recent fighting game with online multiplayer capabilities, Street Fighter 4, you will see different results:

http://www.xbox.com/en-US/games/s/streetfighterIV/

As you can see, Street Fighter 4, a fighting game with online one on one, has 2 Players on the online feature list but nothing more. So, we know 2 Players means actual one on one action that we are used to from other past iterations of the series.

When you compare again to another game, this time NHL 09 the last effort by EA Sports Canada (the developers behind Fight Night Round 4), you get a different picture:

http://www.xbox.com/en-US/games/n/nhl09/

Again in there you can see Players 2-12 listed as online AND Xbox Live Co-Op as an online option as well. This is closer to the online features listed by Xbox.com for Fight Night Round 4.

What does this mean? Perhaps nothing. Perhaps it is a mistake by Microsoft or EA Sports. Yet, what if we indeed have some Online Co-Op component? What could it be? Would it be the Spectator Mode many fans are waiting for?

Speculate and post on the comments.