However, despite a five-game unbeaten run that has seen Los Rojillos rise to seventh in the table, Mendilibar is still looking for more from his players when in possession.
He told the club's website: "Our mentality is good and although our play could be better or worse, we are difficult to beat.
"We have to keep believing in what we are doing, you are not always going to play well, or badly, but you must always try to get something from the game.
"I think we make life difficult for the opponents. However, with the ball we lack something; we need a little more calm and I hope we will develop that."
Mendilibar is again without the injured quartet of Marc Bertran, Ruben Gonzales, Masoud Shojaei and Ion Echaide but should have Raul Garcia back after he missed last weekend's 1-1 draw with Malaga.
Villarreal surprisingly sit above the relegation zone only on goal difference and Juan Carlos Garrido has recognised the importance of a win before the two-week break for Christmas.
Speaking to the club's website, he said: "The match against Osasuna is very important to show that we have made steps toward recovery.
"The most important thing is to have confidence in yourself, but in football confidence comes with results. I believe strongly in this team and I am sure better results lie ahead."
However, Garrido is wary of travelling to the Reyno de Navarra where Osasuna have yet to be beaten this season.
"You always have to give Osasuna respect when they are at home," he said.
"Their game is very intense and they play a type of football that is very difficult to counteract.
"There is always a great atmosphere and this motivates the players a lot, this passion ought to also give us extra incentive.
"The numbers say that we don't win away from home and therefore we have to change our attitude to get better results on the road. We need to do more to change the team's mentality."
Mateo Musacchio is expected to return to the Villarreal defence after serving a one-match suspension against Real Sociedad last weekend.