The pair have been earmarked as two of City's more valuable assets in terms of generating transfer revenue, with Clingan having been the subject of Premier League interest in January and Russell having been signed in more affluent times and likely to be among the higher earners at the club.
Butterworth said the duo have attracted interest and would be left behind so the rest of the squad could be 'fully focussed' on pre-season preparations. It is expected that the money brought in for either or both of the central midfielders will be put towards key positions still vacant, notably the Alan Lee-shaped hole in attack and the Lee Croft and Darren Huckerby-shaped vacancies on either flank.
Meanwhile Dejan Stefanovic will also stay behind as he continues his rehabilitation from the knee injury that ended his previous season last November.