Since Van Der Sar's return from injury, both Tomasz Kuszczak and Ben Foster have been relegated, with Van Der Sar being treated as a walk-up starter despite Kuszczak's strong performances. Foster was given his chance early in the season to show what he can do, and he didn't perform anywhere near as well as a #1 United keeper should. Since then, we've seen next to nothing of him.
A while ago we saw Darron Gibson starting on a semi-regular basis, and the goals he scored certainly didn't do him any harm. However, we have not seen much of him since then. Anderson is in a similar category, and could be on the way out. Also, let's not forget Rodrigo Possebon, who has of course been setback by his less than successful loan spell at Braga.
Since his arrival at the start of the 08-09 season, Dimitar Berbatov has been subject to scrutiny about whether he is the type of player that is required at United. For most of this season, he has been starting alongside Rooney, however as the 4-3-3 formation is becoming more frequent, Berbatov has been left out of the squad more frequently. Same story for Michael Owen, although he was always the #3 striker, the role now seemingly taken by Mame Biram Diouf.
Big question-marks hang over these players' heads, bar Kuszczak, and in some of their cases, if they don't improve this half of the season, they could be on their way during the summer transfer market.