José Mourinho is facing the uncomfortable and potentially damaging prospect of going into the new Premier League season without Frank Lampard and David Luiz, while Juan Mata is also an injury concern.

The Chelsea trio have played limited roles because of injury and a lack of match fitness during the club's four-match tour of the United States that comes to a conclusion here against Roma on Sunday.

With the season opener against Hull a week away, losing such key players for the start of the campaign is a problem the Portuguese can do without.

Lampard, who has been struggling with an Achilles injury that has restricted him to 45 minutes against Real Madrid in pre-season, is the Chelsea manager's biggest concern. While the initial injury is showing signs of recovery, the 35 year-old's lack of match fitness is holding him back.

Mourinho concedes the midfielder is not ready for the resumption of the Premier League and will carefully assess him against the Italian side before return to London.

Surprisingly, considering his total lack of match-time this summer, the England manager, Roy Hodgson, has included Lampard in the squad to face Scotland next week – a decision Mourinho is comfortable with. There could well be a different reaction from the manager if his injury is worsened by playing at Wembley and, asked if he believed the midfielder was ready for the start of the season, Mourinho said: "No, he still has to train. He has to play against Roma. He played 45 mins against Real, maybe he plays 60 against Roma. He is in the England squad so it will be good if he plays a part against Scotland.

"He is getting ready. But his pre-season has seen him train for a week and then stop for two weeks. He is coming back again, we are calm. We have to be calm. We know the stages of recovery. His first minutes of pre-season have been against Real Madrid."

The situations with David Luiz and Mata are equally precarious for Mourinho. The Brazilian has struggled with a hamstring strain problem since the end of last season and, like Lampard, has played only intermittently in the US.

David Luiz came on for 30 minutes in Indianapolis last Thursday against Internazionale and has not been seen on the pitch since. The way Mourinho defiantly and instantly rejected a £35m bid from Barcelona for the 25-year-old proved just how integral a player he will be this season.

Likewise with Mata who, like David Luiz, missed Chelsea's tour to Asia because of his involvement in Spain's Confederations Cup campaign. They stayed behind at the club's DC base instead of travelling to Miami to take on Real Madrid on Wednesday. "They are important players," said Mourinho. "The team with David Luiz and Mata is a better team. But again this is not a problem, we don't risk players in pre season.

"Mata had a little thing, we didn't take a risk. David had an injury from before the Europa League final and he still has little things with it, so we stop.

"If David misses the start of the season then its only because of his injury. That's why I'm not risking him. He had a good session in DC with the fitness guys while we were in Miami. So, hopefully, there will be no problems."