Jaaskelainen kept another clean sheet in the draw against Wigan in midweek and Coyle is delighted with the veteran's form.
"He has been a top-class goalkeeper all his days and still is. He has a big role to play at this club, " he said.
"Defending is a team game but if the players are breached they know there is a top-class 'keeper to make saves.
"The shut-outs are pleasing but equally we have to take our chances at the other end. It is a case of putting those two things together."
Coyle could get a lift with the possible return of Croatian striker Ivan Klasnic. The 30-year-old, who has scored six goals this season after arriving on loan from Nantes, is on the mend after a calf injury.
He last appeared in Bolton's only win under Coyle and that was against the manager's former club Burnley last month.
Coyle said: "Klasnic has not trained with the group yet but he may join in today. If he does I will have to look at that.
"What I can't do is take a chance with him and have him miss another two or three weeks because he is a natural goalscorer. He will be important for us in the run-in."
Bolton have won just one league game in seven since Coyle arrived but he is convinced they can move out of trouble.
He said: "It is so tight at the foot of the table and a real battle. There is hardly a coat of paint between a number of clubs.
"You have to believe in what you are doing and in the players you have. They have shown they can go toe to toe with some of the best teams in the country.
"We are coming up against a very good Blackburn side, with a terrific home record. But want to go there and put our own stamp on the match."