José Mourinho admits Chelsea are “in trouble” because of their mounting injury problems. While the manager hopes to have Diego Costa back for Saturday’s Premier League home game against QPR, he pointed to the injuries to Ramires and Loïc Rémy, plus the short turnaround between Sunday’s game at Manchester United and Tuesday’s Capital One Cup trip to Shrewsbury, as evidence of the difficulty he faces.

“I have only one day, we travel to London and we are travelling to Shrewsbury. We are in trouble because we have so many injured players,” he said. “It is even more difficult for us to go. We have to go. We now have a difficult match. Because they are doing very well in their league and doing very well against superior teams in the Capital One Cup. It’s a big day for them. We know it will be difficult for us. But that’s football.

“Every game is important. Shrewsbury is not a friendly. We have to play matches with respect and the best way to respect Shrewsbury is to go there with a good team. Not to go there with a weak team and lose. It is to go there with a good team –if they win, they win, but they win against a good team. We are in a difficult situation with regards to today but, when you look at the players who didn’t play – Schürrle, Salah, Zouma, Aké, Mikel – these boys are obviously going to have to play.”

André Schürrle is likely to play as the lone striker against Shrewsbury because Rémy is out for two weeks with a groin injury and Costa is hampered by a hamstring complaint. Didier Drogba played the full 90 minutes against United and, at 36, might struggle to feature again so soon.

Costa’s fitness problems are of most concern to Mourinho. The Spain forward, who has been troubled by the niggling injury all season, was in hospital with a stomach virus last week but also has a groin strain apparently picked up on international duty. He has failed to train properly since returning to London after Spain’s Euro 2016 qualifiers against Slovakia and Luxembourg, in which he played all but eight minutes.

His return for Saturday’s derby would come as a big boost. “I think so. QPR, one week more, I hope so,” said Mourinho, when asked about Costa’s availability for the game at the weekend.

“The virus is fine. It was hard when Costa went to hospital and obviously it doesn’t help to recover from the injury. But he didn’t come [to Old Trafford] because of the injury, not because of the virus. He aggravated the hamstring because he played two matches in three days and was not with us.”

Nemanja Matic confirmed Costa pulled out of the squad on the day before the match at Old Trafford. “We found out Saturday,” said the midfielder. “He trained with us but I think he felt some more pain and the club didn’t want to risk him. Of course we need him but the most important thing is to be healthy and to be prepared for the next games. We have a lot before the end. We need every player fit.”

Despite being held to a 1-1 draw by United, courtesy of Robin van Persie’s added-time equaliser, Chelsea have a four-point lead over Southampton and are six ahead of Manchester City. Matic is clear Chelsea are the side to catch. “It’s a good feeling but also a big responsibility because now everyone wants to win against us; they have extra motivation,” he said. “It’s normal. We have done well and deserve to be in this position.”

Of the draw with United he said: “Every point is very important for us, especially when you’re playing against teams like Manchester United. They are strong and everyone knows they’re a big club. Old Trafford is not an easy place to get points. In the end you never know what is going to decide the championship but maybe this point will be crucial for us.”

After nine games Chelsea remain unbeaten and have already visited United and City. Matic said: “It’s good for our team. It gives us confidence. There are not a lot of teams who have gone nine games without a loss – we are the only team in the league to have done that this season. We are happy because of that.”