Eddie Jones remains hopeful Marcus Smith will be able to feature for England against Tonga on Saturday despite the fly-half struggling with a leg injury.
Harlequins star Smith, who won his first two caps during the summer's wins over the USA and Canada, has been limited to ball-handling in training so far this week due to the injury.
Jones is eager to give the 22-year-old another opportunity in England's first Test of the Autumn Nations Series and while he concedes that may have to wait until the clash against Australia, the head coach is still planning on having him available to face Tonga.
"We're being conservative with him, but we're cautiously optimistic that he'll be right to play," Jones said.
"We are keen for him to be involved in the game. If we don't get to see him this week, we will get to see him next week.
"It's not frustrating, it's part and parcel of preparing a team. Players pick up small knocks and he'll recover well."
Should Smith be unavailable, Jones has the option of moving skipper Owen Farrell to fly-half from inside centre, while full-back George Furbank has played in the No 10 role for club Northampton Saints too, and has been spoken of in glowing terms with regard to his potential in the position by the Australian in the past.
Jones has another injury issue in the halves as uncapped Sale Sharks scrum-half Raffi Quirke has joined Harry Randall (hip flexor) on the sidelines, leaving Ben Youngs and recent call-up Alex Mitchell as the only fit No 9s.
Injuries have affected other areas in the backs as another summer debutant, full-back Freddie Steward, has suffered a leg problem as well and is a doubt for Saturday's clash at Twickenham.
Max Malins, another who could potentially take the No 15 shirt and is the leading try-scorer in the Gallagher Premiership so far this season with seven, has also been ruled out along with winger Louis Lynagh, who was drafted into the squad along with Mitchell over the weekend.
"We had Max Malins and Raffi Quirke come into camp with injuries," Jones said. "They've been rehabbing but won't be considered for selection for the Tongan game, but we're hopeful they'll be fitter further down the track.
"Louis came in a bit beaten up after the game and so he hasn't been able to train with us. With Max unavailable because of the injury he brought into camp, we just thought we needed additional cover, but unfortunately Louis is injured as well.
"We hoped he would recover but he hasn't been able to train on Tuesday. It's been a difficult situation for the young lad."
Along with Furbank, the versatile Henry Slade would be another likely candidate Jones, who names his England team to tackle Tonga on Thursday, would consider should he be forced into a change at full-back.
Seven return to clubs
Meanwhile, Jones released seven players back to their clubs on Tuesday afternoon as he slims down the squad ahead of naming the 23-man matchday group to face Tonga.
Among those were No 8s Sam Simmonds and Callum Chick. It could therefore come down to Jones choosing whether Tom Curry will reprise the position he has previously featured in for England or if Alex Dombrandt, who won his first Test cap against Canada in the summer, will get another start.
Hooker Nic Dolly, flanker Lewis Ludlam, second-row George Martin, full-back Tommy Freeman and the injured Lynagh have also been sent back to their clubs.