Joe Rankin-Costello has suffered another injury setback with a further frustrating period on the sidelines expected for the utility man.

Rankin-Costello saw his comeback from a broken foot sustained in April hit by a hamstring strain, but a similar injury on the opposite leg will now delay his latest bid to break into the side.

The 22-year-old played three times for the Under-23s as part of his previous comeback and got his first minutes since April under his belt as a second half substitute in the 7-0 defeat to Fulham.

He was left out of the squad for the visit of Sheffield United, not due to injury, with his latest setback coming in training earlier this week.

Hamstring injuries have hindered Rankin-Costello’s progress since breaking into the side last year, but it was a broken foot sustained at Wycombe Wanderers in April that ended his 2020/21 campaign.

“Rankin-Costello won't be available," said Mowbray.

“He tweaked his hamstring again in training which is a massive frustration for him and for us.

“He has to get on with it and keep going, to try and be mentally tough. Somewhere down the line there will be a good day for him but it's tough at the moment.

“All hamstring (injuries) are a problem, you have to be careful in your rehabilitation so I suspect he will miss the next few weeks.”

Mowbray confirmed that Daniel Ayala and Harry Pickering are back in training following their respective calf lay-offs.

Pickering has been out since the 1-0 defeat at QPR last month, with Ayala limping out of the Reading win in the next game.

Both are in contention to feature at Bristol City, but Sam Gallagher isn’t yet ready to be involved.

"I ask the physio everyday and he's just not ready yet," Mowbray added.

"I see him on the grass sprinting, making runs and whacking the ball in the net but if he's feeling it, he's feeling it.

"With the type of injury he's got, which is a strain, it's pertinent to ensure he's pain free before we put him back."