PFA Player of the Year as Leicester stunned the world by winning the Premier League last term, Mahrez has struggled to replicate that form, with the defending champions languishing in 14th position.
Mahrez scored a first-half penalty on Saturday but it was another frustrating outing as Leicester crashed to their sixth defeat of the season, beaten 2-1 at Watford.
And Ranieri is weighing up whether to drop the Algeria international - on the shortlist for this year's Ballon d'Or - in a bid to help him rediscover his form.
"Of course we have to do something, have to study something, because the opponent now knows us very well and we can't continue only with Riyad and to give him all the responsibility," said Ranieri.
"You watch the match and every time Riyad gets the ball he tried to do something special. The opponent is very careful when he receives the ball, always three opponents were close to him.
"I try to say to him play simple, but sometimes he takes the responsibility to do something for the team because he is our quality player.
"His season is okay, because in the Champions League he is playing well and also he is trying to do his best in the Premier League."
Mahrez has scored twice in 12 Premier League appearances this season, having netted 17 goals in 2015-16.