He's had 6 months to get up to speed and still Sam said he's not showing enough in training to warrant a place in the squad. I suppose he's a Rooney/Sig-lite and if he can't find a place for both of them at once then he's not going to find a slot for Klaassan.
He's not really had 6 months to get up to speed though, you can only do so much in training to try and impress but the only way he's really going to get sharp is playing games. He hasn't even been given a game by Allardyce other than Limassol and Allardyce wasn't even at that one. A total of ten games at an average of 43 minutes per game isn't really getting the chance to learn the league and get any sort of match sharpness.