Cambridge, who is arguably manager Steve Fallon's best signing in recent years, will feel unlucky with his release after all the hard work he and Neil Kennedy put in to get the club to where they are today.
It has been a recent dry spell of appearances for Cambridge that convinced Fallon to let the Stutes star leave.
Fallon told cambridge-news.co.uk : "Ian has had a couple of great seasons - especially the year we won the Southern League - when he and Kennedy were electric.
"But things change and so do players priorities.
"It's fair to say that Ian has not featured as much as he or I would have liked, and with what we are looking at for next year it allows Ian to find a new challenge."
Roberts' departure is one of no real surprise as he has failed to feature on a regular basis since joining from Aylesbury United in November 2005.
It was a similar case for both former England semi-professional international McDougald and Welsh under-21 cap Davies, as they both failed to make a major impact on the Stutes impressive season.
Source: http://www.confguide.com/newsArticle.do?id=6428