Antonio Conte believes that Diego Costa has finally learned to control himself and become “an example” to his Chelsea side.

The Spanish striker became something of a liability in his first two seasons at Stamford Bridge due to his irascibility which repeatedly got him into trouble with referees and the authorities.

But now Conte believes Costa has changed and has praised his overall attitude and demeanour after declaring the 28-year-old fit to play at Middlesbrough on Saturday despite missing his country’s matches with Macedonia and England, picked up while playing against Everton.

Costa has scored nine times in Premier League games but his manager believes he brings far more than just goals to the side.

“I think Diego is a very good player,” said the Italian. “It is important for me to see that every game Diego works a lot with the ball and without the ball. He’s an example for all and I want him to continue that way.

“If all players think this way, we’ll be a good team and tough to play again.

“Diego shows emotion but he can control himself. It’s fantastic.

“Diego is improving a lot in a lot of aspects. For me now he’s one of the best strikers in the world.

“He must continue working in this way, with the commitment and work rate. He’s fantastic to see his work rate in games and training games.”

Chelsea are in outstanding form with five straight league wins and there is an air of positivity, especially with Costa’s fitness boost and similarly positive news about Eden Hazard.

“Costa had a bit of an injury and started to train on Wednesday,” confirmed Conte. “His physical condition is good. He can play. Eden only had a tackle, and he recovered very well.

“I am always worried when I see there is a probability that one player is not able to play. You are a bit worried but it's important to play for the national team. So far we were lucky. Not one player came back injured.”

Chelsea vs Everton player ratings Show all 22 1 /22 Chelsea vs Everton player ratings Chelsea vs Everton player ratings Kepa.jpg Wasn’t asked to do much, especially in the second half but a clean sheet is a clean sheet. PA Chelsea vs Everton player ratings Azpilicueta.JPG Created chances going forward and was as solid as ever defending the attacks from the left wing. REUTERS Chelsea vs Everton player ratings Rudiger.JPG Made some mistakes in the game, gave the ball away too easily and got involved in some poor clashes. Got booked for nonsense argument with Bernard but did well to keep Richarlison at bay. REUTERS Chelsea vs Everton player ratings Luiz.JPG Tried to play balls through the centre of the pitch to the front men. Blocked off Coleman to allow Alonso to run into space off the free kick. Action Images via Reuters Chelsea vs Everton player ratings Alonso.JPG Really threatening from the left wing and hit a spectacular volley that was denied by Pickford. Action Images via Reuters Chelsea vs Everton player ratings Kante.jpg With Jorginho was unable to comfortably play the ball where he wanted but that was down to the pressure put on him by Everton. AP Chelsea vs Everton player ratings Jorginho.JPG Got challenged to the ball frequently by Sigurdsson and came off worse for it. Most of his influence came by playing from his own half. REUTERS Chelsea vs Everton player ratings Kovacic.JPG Tracked back and defended well against Richarlison and played some good balls out wide when switching the play. REUTERS Chelsea vs Everton player ratings Hazard.jpg Turned up the tempo in the second half, firing shots from range and working the ball into the box from the wings and the middle of the pitch. AP Chelsea vs Everton player ratings Willian.JPG Found Alonso with a pitch perfect free kick and combined with Morata and Hazard to create an opening in a solid Everton defence. In the second half who two or three chances to put Chelsea in front but narrowly missed them. REUTERS Chelsea vs Everton player ratings Morata.jpg Sent Willian in behind Digne with a great ball through the defence but wasn’t clinical enough in front of goal. PA Chelsea vs Everton player ratings Pickford.jpg Stopped Alsono’s volley with a diving save to keep things level in the first half and was under serious pressure in the second half but made some stellar saves to keep a clean sheet. PA Chelsea vs Everton player ratings Coleman.JPG Played well down the right and linked up with Walcott and Richarlison in the first half, had a lot of defending to do in the second 45 minutes and did it well. Action Images via Reuters Chelsea vs Everton player ratings Keane.jpg Started a little sloppy but came into his own as the match wore on. Everton directed their set pieces at him, but he couldn’t direct a header towards goal. To come to Stamford and get a point is a good effort. AFP/Getty Images Chelsea vs Everton player ratings Mina.jpg Got booked for a challenge on Hazard, it was a strong one and probably deserved a card, but it set the tone for solid defence from Everton. Getty Images Chelsea vs Everton player ratings Digne.JPG Very good. He defended well at left back and created options for Everton on the wing. His delivery from set pieces was accurate and just needed better finishing quality. REUTERS Chelsea vs Everton player ratings Andre-gomes.jpg Looked composed and in control in the mid-field with Gueye they were able to play out from the back with ease. Getty Images Chelsea vs Everton player ratings Gueye.jpg Closed down the Chelsea men and won the ball back in mid-field. With Gomes he manoeuvred the ball forward for Everton. AP Chelsea vs Everton player ratings Walcott.jpg Combined well with Coleman in the first half but had to defend in the second when Everton were under the pump. Getty Images Chelsea vs Everton player ratings Sigurdsson.JPG Asked to limit the influence of Jorginho and was successful in that role. He also played some beautiful passes into the wide men to spread Chelsea’s defence. REUTERS Chelsea vs Everton player ratings Bernard.jpg Missed a great chance in the second half to put Everton in front and from then on Chelsea dominated. Played well in the first half but his miss is unforgivable. PA Chelsea vs Everton player ratings Richarlison.JPG Held the ball up well and caused problems for Chelsea’s defence. Rudiger in particular found the battle tough and it’s honours even for the match. REUTERS

Conte though seemed unnecessarily worried and is wary that such a positive run of results may soon be coming to an end.

“We are working to avoid a loss of momentum,” he said. “We are working to find the right concentration and focus.

“On Sunday we know we'll have a tough game against a strong team who drew with Arsenal and Manchester City.

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“I must be honest, there is this possibility, to stop our momentum. But we are working very hard to avoid this.

“In this situation it's important to keep the concentration very high. It's normal that the focus, the concentration, is a bit low in this situation.

“I'm worried, I'm worried to keep this concentration. I'm worried to keep that high intensity and right spirit in training. That's the most important thing. When you win five or six in a row, that's what you think about.”

Costa's form has helped Conte's Chelsea rise up the Premier League table (Getty)

Meanwhile Conte has dismissed suggestions that Oscar has no future at Stamford Bridge despite not starting a league match since September.

“Oscar's future is Chelsea,” said the Italian. “Chelsea, full stop. For me, Oscar is an important player in the squad. He's in good form.

“It's logical I have to take the starting XI every week, but Oscar is a great player. For me, he stays at Chelsea.