Riley suffered the injury in training on Monday and while Coyle is not putting a timescale on his recovery, it will not be in time for this weekend.
"Just when you think you have turned a corner, you suffer another little setback," Coyle said."It puts more onus on Dedryck, who is back in light training."
Boyata has not featured since a 2-0 defeat by Sunderland in October, when he sustained ankle ligament damage.
It was initially suggested he would be out for six weeks, but the Belgium international - who celebrates his 21st birthday on Monday - is slightly ahead of schedule, giving Coyle some hope for this weekend.
"We have to let it run its course," Coyle added. "We cannot put anyone in if he is not fully fit, so we will see if there is any reaction to his training. Prior to his injury he was in a terrific run of form. We know what Dedryck is all about. I am sure he is destined for great things."
Meanwhile, Coyle is ready for another frenzy of speculation surrounding Gary Cahill, who was the subject of a bid from Arsenal in August which Bolton rejected as derisory.
"That is the nature of the job," Coyle said. "Gary Cahill is an outstanding player. As I have said, whatever comes in January, we will deal with it then.
"Between now and then, Gary has to be focused and doing his job to the best of his abilities, as he always has done, both for himself and his international aspirations, and the team.
"Gary is a top player. If there are people who might be interested come January, so be it. But Gary has to be performing for Bolton. If he is, the rest will take care of itself in January."
Source: PA
Source: PA