Would think its an injury. Even though Berbatov is clearly no longer first choice, are we really likely to get a better backup than him? Especially one that can play either of Rooney's or Hernandez's role - not quite in the same way no, but he can be the support striker receiving the ball from the midfield or he can be our goal getter like this season. I'm pretty sure even a backup player who can play both roles well enough to be playing for us is going to be expensive. A lot more than we'd get for Berbatov at this point and with us needing to sort the keeper and midfield before we worry about up front, would we have the money? Surely not.
The issue there would be the wages. But again, it would surely be hard to find a better stand-in than the league's top goalscorer and if we did sign someone of a similar quality they'd probably want fairly high wages if they are going to be seen as a backup. I'm sure the wages would come down a bit but how much, who knows?