Although the four-year-old also holds an entry in the valuable Dubai Duty Free Handicap at Newbury, the Newmarket handler is keen to make the one-mile-one-furlong prize on September 30 his main target.
Chiefofchiefs was pulled up on his seasonal return at Windsor in May, but the son of Royal Applause has since won three times from six subsequent starts.
Fellowes said: "He has got both races as options and they would both be lovely races to win, but the Cambridgeshire is very much plan A.
"He is off 88 and last year 89 got you in, so he will need to win again to get in. That is why we brought him back quick at Windsor, but the plan didn't quite come off.
"He has had a lot of racing this year and we are just freshening him up now before taking a look at a race in the first week of September to try pick up a penalty to get in.
"It is a risky ploy but I think he is will be well handicapped and if he does get in and it will be the perfect race for him.
"It is not the be all and end all if he doesn't get in, but it is a lovely target to aim for."
Plans are in place to give stablemate Endless Acres a shot at the Cesarewitch following his return from a mid-season break.
The four-year-old has not been seen since he finished second in the Ascot Stakes at the Royal meeting in June.
Fellowes said: "The plan is to go straight to the Cesarewitch with him. He has had a two-month break and he is back cantering.
"He ran a huge race at Ascot on ground that was too quick for him and it was good to see that form franked by Magic Circle at York as we have beaten him twice this year.
"He is a very progressive stayer, but he is still a baby.
"Whatever he does this year will be a bonus as I think he will be a very nice horse next year."