"For the past few matches we've played 4-5-1 and Carlton Cole, at this stage, is more suited to that role than Dean.
"I spoke to him before the Manchester United match and I think he understood. After that result it was no surprise we stuck with the same system against Arsenal, although it wasn't as successful because we conceded an early goal.
"He suffered a bad injury and we have to manage his fitness carefully. I believe we're doing that.
Ashton is said to be considering his future at the club as his remaining contract only runs for another 18-months and contract talks seem no closer to opening.
Curbs continued, "Dean had an uninterrupted run of games when he came back until he injured his knee. Since he's returned, he's been okay again with no other problems.
"We've had a lot of games in a short space of time and I didn't want to overload him. He should be nice and fresh now as we go into Saturday's FA Cup tie against
"I've no problem with Dean and he remains an important part of our plans."