How has he 'lost his edge'? I think Yakubu needs to regain his confidence and match sharpness but his injury hasn't effected any area of his game. He isn't any slower than he was during the 07-08 season and he's never relied on pace anyway. He's an intelligent footballer with good physical strength, that hasn't changed.
And he did some decent things when he came on today, held the ball up and made one excellent pass to Baines towards the end of the game. But Neiler's right, it all comes down to how he responds to not being an automatic starter, there's competition now, he's got to stand up and be counted. If he does that then we'll have some serious competition upfront, Yakubu is and always has been a quality player.