Neither was expected to practice at the start of training camp after having offseason medical procedures. Sanders had shoulder surgery, while O'Neil underwent sports hernia surgery.
Team president Bill Polian also announced several housecleaning moves Monday.
Tarik Glenn, who announced his retirement last week with one year left on his contract, was placed on the reserve/retired list.
Defensive tackle Quinn Pitcock, a third-round choice out of Ohio State, was placed on the reserve/drafted-unsigned list because he has not yet passed his physical. Pitcock was the only draft pick missing from Monday morning's first workout and is expected to join his new teammates in the next couple of days.
Coleman, a 5-foot-11, 195-pound cornerback out of Clemson, was not drafted in April.
Polian said it's likely undrafted rookie receiver Michael DePriest would be placed on injured reserve later this week.