Healy, who is currently a free agent, has been omitted from O'Neill's squad for the next World Cup qualifier.
"David still has loads to offer I believe," O'Neill told reporters. "I think if he finds a manager who has faith in him and gives him an opportunity, he is more than capable of scoring goals for club and still at international level.
"I think it's very difficult for any of our players that are unattached at the moment, [the players] agree with that."
Northern Ireland play Russia at Windsor Park on August 14.