Chelsea boss Frank Lampard has said the club are "still searching" for the best way to improve Christian Pulisic's fitness record after the USMNT international was ruled out of Saturday's trip to Newcastle United through injury.

Pulisic is continuing to struggle with complications arising from the hamstring problem he sustained in the FA Cup final defeat to Arsenal on Aug. 1.

- Stream ESPN FC Daily on ESPN+ (U.S. only)

The 22-year-old has been missing since aggravating the issue during the warm-up prior to Chelsea's game at Burnley on Oct. 31 and spent the international break at Cobham attempting to step up his recovery with Lampard particularly wary of pushing him into action too soon.

Lampard said in September that Chelsea were attempting to devise a more tailored training programme to ensure he avoids a repeat of the persistent injuries he sustained at Borussia Dortmund prior to his £58 million move to Stamford Bridge last summer.

Pulisic is slowly increasing his training load this week but will not be available for the match at Newcastle on Saturday lunchtime.

"With Christian, we are still searching [for an answer]," Lampard told a news conference on Thursday. "He is in a position at the moment where as I said he's had a problematic injury and I think it is normal.

"Not every player is different. I think Christian had an issue before coming to us, some muscular injuries. He's had them again. Everything about Christian, how he is around the training ground, how he prepares, how much he wants to play, is perfect.

"So we need to try and find the right balance between playing, resting and maintenance during the week to try and get the best out of him. He is a young player still. It is not abnormal.

"We will find a solution and I don't want to make more of it than it is because we want as many games of Christian as we can possibly get because of his ability. But at the minute, he's injured so in the short-term it is a work in progress. But we have a great medical team here and we are very much joined up on the idea of getting the best of Christian by getting him fit as much as we can."

Lampard has yet to see several players returning from international duty and with the shortest recovery time possible before travelling to the north-east for the first Premier League game of the weekend.

Kai Havertz is training again after testing negative for COVID-19 but earlier positive tests mean he is unlikely to be fully fit while Thiago Silva did not train on Thursday having only just returned from Brazil.

Ben Chilwell is a doubt after sustaining a minor injury while with England -- although he's expected to be fit -- but Lampard voiced his frustration at the 12.30 p.m. kick-off time giving his players minimal preparation time, especially with a flight to France on Monday ahead of their Champions League clash in Rennes.

"I'm concerned because across the Premier League the injuries are going up," Lampard added. "Muscle injuries are going up, the numbers are there if the Premier League want to go and look at them closely.

"So it is clear. There is a correlation of games, game after game after game. Zero preseason, the schedule is tighter.

"Throughout the season there will be these really busy patches and if we want to handle them as best we can, if we want to look after the players and get the product as well as we can, change the time of 12.30. Change the time. That's not a difficult conversation for me to have.

"The amount of things we change due to COVID and Project Restart and now in this season that we have to change because these are incredible times, then we have to continue looking for the best way to change it. So the answer is: stop talking and act upon it."