The Italian gave Davies his first international call-up at the age of 33 and the Bolton striker made his debut in Tuesday night's Euro 2012 qualifier against Montenegro.
And although the Bolton skipper posed plenty of problems off the bench, Coyle felt a 20-minute cameo just wasn't long enough for Davies to make a difference as England had to settle for a 0-0 draw with the Balkan minnows.
"This game is all about opinions but my own take on it is that if he were on earlier, England could have won the game," he said.
"What he was asked to do, he did very well. I would have loved to have seen some crosses coming in from wider areas for him to attack in the box.
"You just knew his presence in the box really unsettled them.
"Kevin was told to try to knock things down in the box and he did. On another day, they might have resulted in a goal.
"Wayne Rooney came very close to winning the game after Kevin came on, there were a few things flying about around the box."
England do not have another qualifier until March but Coyle has urged Capello to keep Davies involved for the friendly against France on November 17 rather than casting him aside as a one-cap wonder.
"I think there is a case for it," added the Bolton boss. "It will keep him going until the qualifiers come about.
"All he can do is keep playing well for his club. What he has to do now is kick on. He won't rest on his laurels.
"You want to go and add to that and the next qualifier is in March so he needs to keep his form up and really give Mr Capello something to think about when that comes about.
"He's got a little injury but we hope he'll be OK for Saturday and he's delighted to have finally got that elusive cap.
"It would have been a travesty for him to end his career without representing his country at full international level."
Bolton team-mate Gary Cahill was also on the bench but was not given the chance to add to the first cap he won in the qualifier against Bulgaria last month.
"As a manager of one of the smaller Premier League teams, we were so proud to have him and Gary Cahill in the squad," Coyle added.
"He got an incredible reception from the crowd when he came on and, hopefully, that's given him a real boost.
"I'd love both Kevin and Gary Cahill to be in future squads but obviously to do that they need to be playing at a high level for Bolton Wanderers.
"However, I have no doubts they will both do just that."
Source: Team Talk
Source: Team Talk