Defensive duo Aiden Flint and Dani Ayala are both set to miss Middlesbrough's FA Cup tie with Peterborough.
Flint was withdrawn from the squad to face Derby County after picking-up an injury in the warm-up, while Ayala has picked up a knock during the trip to the iPro Stadium.
That means that Tony Pulis will have to do without two of his star performers for the game against Steve Evans' side, with the manager admitting Flint was a 'major concern'.
Speaking at his pre-match press conference, the Middlesbrough boss said: "We've picked up some injuries and a disappointing one which is Flinty.
"It looks like he will be out for a few weeks.
"Ayala has also picked up an injury and if you add that to Shotton - it's a bit of a worry for us defensively.
"We're a little bit concerned at the minute in terms of how one or two of them are.
"Ayala, Shotton and Flint definitely won't be involved tomorrow.
"Flinty is a major concern for us and Shotton is getting there but again, that's taking time.
"Dani has picked up an injury at Derby."
Their absence hands Tony Pulis something of a headache ahead of the visit of the League One promotion chasers - and he has confirmed he will turn to youth in a bid to plug the gaps in his squad.
Nathan Wood is expected to start at the Riverside Stadium, while Pulis also revealed that new signing Rajiv van La Parra will be handed an opportunity to impress too.
"I think tomorrow we'll have the youngest player that has ever played for the football club [Wood] in the squad, and the oldest player that has ever played for the club [Dimi Konstantopolous] in the team," admitted the Middlesbrough chief.
"He [van La Parra] hasn't played much football and we need to get him fit.
"He will start tomorrow."