Chelsea head to Middlesbrough on Sunday buoyed by the knowledge that star men Diego Costa and Eden Hazard have both been passed fit as the Blues resume Premier League duty after the international break The pair had been considered doubts but manager Antonio Conte has confirmed they had each received the all-clear as the West Londoners bid for a sixth straight league win. Costa’s fitness was of particular concern after the forward suffered an injury at Everton which meant he missed Spain’s international matches with Macedonia and England. But he is now at the service of Italian manager Conte, while midfielder Cesc Fabregas is also fully fit following a muscle problem. “I have all the players available,” said Conte. “They are in good form. Costa had a bit of an injury after the game against Everton, and started to train with us on Wednesday. But his physical condition is good. “Hazard is fit, yes. It was only a tackle. But he recovered very well. Fabregas is in good shape. He’s available for Sunday, for sure. “I’m always worried when I see that there is a probability that one player of my team, of my squad, is not able to play the game. “But, in this case, when there is an international break and you are a bit worried for your players it’s important to play for the national team. “Until now, so far, we were lucky because no one player came back from the national team injured after the international break,” former Italy manager Conte added. Conte believes he is building a new-look side with his men second in the Premier League over the international break following the disappointment of failing to qualify for European football last season. “I see a chance to build something important with Chelsea here, a new method and philosophy,” he said. “These are the most important things. Then it’s logical, when you play this championship, that you want to fight until the end. To win the title, or for a place in the Champions League. “It’s important now to work with the players, to continue to build something of importance for Chelsea for the present and the future.” Conte, meanwhile, insisted Oscar still has a future at Stamford Bridge despite the midfielder failing to start a league game since September. “Oscar’s future is Chelsea, Chelsea, full stop,” said the manager. “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.” Aitor Karanka celebrates three years in charge of Middlesbrough with the northeast side looking to build on the point earned in a 1-1 draw at Manchester City before the international break. Middlesbrough are unbeaten in three games, and the Spaniard said: “When we came here three years ago, the team was not in a good way, and we’ve made progress. “The chairman, the club and the crowd deserve to be in the Premier League to face challenges like this one we have coming up against Chelsea. “It’s another big game against a side that I believe will be challenging for the title, and it will be the latest gauge of how far we’ve progressed.” Middlesbrough captain George Friend (knee) is an injury doubt, and Daniel Ayala (knee) remains sidelined. Gaston Ramirez and Cristhian Stuani will be assessed before Karanka makes a decision on whether to include the Uruguay pair after their return from long-haul trips on international duty.