The Roman Senate. They were instrumental in getting rid of both Julius Nepos and Orestes - if Odoacer goes against his backers' wishes, they will make his life hell. Expect urban mobs to be driven into a frenzy in the major cities and the senators to finally accept that the people working their latifundia sometimes have to join the army. Meanwhile, Odoacer's men aren't getting paid, and while loot may keep some happy, not all of them will get to enjoy it, and they may even see whatever possessions they may have being threatened, as the population starts to turn against them.
At this point, individual commanders will see the benefit of switching sides and/or assassinating Odoacer.
Even if Odoacer avoids getting killed or having his main force desert or get defeated (which I find highly unlikely to happen), he will have trouble controlling more than a fraction of Italy, making him extremely vulnerable to even a small-ish expedition launched from the ERE once their civil war ends.
Just my two cents.