Scottish striker Shaw and defender Cotter have made just three appearances apiece since joining the Reds in the January transfer window, with their last ones coming in the League One win at Cheltenham Town in late February.

Former Huddersfield Town midfielder Russell has fared better with nine appearances following his switch from the Terriers.But he has made just two starts, with his last one coming on March 4.

Martin, who joined from Norwich City last summer, has not featured at first-team level since coming on as a late substitute in the 4-1 win over Derby County on February 25.

Duff, whose fourth-placed side visit Lincoln City on Tuesday night, said: "It is tough. Barry and Oli - and even Jon to a certain extent - have come in and the team have been going really well.

"So you are loath to disrupt it, but to be fair to them, they are training properly and getting minutes with the under-21s. You never know; Oli might end up scoring the winner at Wembley.

"You need to make sure he's ready all the time. You look at Ziyad (Larkeche) and he's a perfect example of it.

"I know he went down with cramp, but he's match-ready because of the way he trains and that's what we expect. The players are working hard and it is not a case of 'out of sight, out of mind.'

"They come into conversations and our thoughts in every team selection. But at the minute, we have been going with what we have got.

"They (Shaw and Cotter) are both training and it's a difficult one, you can't keep everyone happy.

"Josh is a little bit unlucky in terms of the six loans and the five-loans rule. With the loans we have got, we have not been able to include him."But it is making sure they are ready. It is the tough part of football, they are coming in and training and not getting into the squad.

"That's what we have got a squad for and we have been lucky with injuries recently in that we have not had many and he had to change the 18."

Larkeche, who deputised for the suspended Nicky Cadden in the 5-1 weekend win at Forest Green, is fine for the trip to face the Red Imps, despite coming off with a touch of cramp on Saturday.

Duff continued: "He is fine, it was just cramp. I spoke to him yesterday and he feels good, so he's come through it and everyone has as well and we have a clean bill of health.

"It was good to (also) get Robbie (Cundy) back on the pitch and it is all good."

Barnsley FC head coach Michael Duff sends out a message to Oli Shaw, Barry Cotter, Jon Russell and Josh Martin