The Dane - who recovered from a shaky start to his Boro career in early autumn - came off with an ankle injury in Saturday's 3-2 loss at Bristol City.

Alex Bangura is now likely to be handed just his first league start since September for the Teessiders, who face a tough visit to Leeds United on Saturday - following their midweek encounter with a play-off chasing rival in North End.

Boro are already light in options in their backline with Darragh Lenihan out for season following Achilles surgery and Tommy Smith also set to miss the remainder of the campaign.

Boss Michael Carrick said: "He (Engel) won't be ready for Preston. How long at this stage we don't know.

"Hopefully, it's a matter of days, but we'll have to wait and see. It's still quite early and fresh and we're still assessing it.

"We seem to be picking up a few (injuries). It was a really unfortunate one and a nasty twist when you watch it back. Hopefully it wasn't too bad and we have him back soon.

"There are two sides to it. There's the disappointment of losing players but the flip side is that is why we have the squad and opportunities.

Middlesbrough head coach Michael Carrick. Picture: Bruce Rollinson.

"That's not forgetting about the injured players but we have a team to pick and someone else will play. We'll work to get the boys back as quickly as we can.

"You never really want to have the issue of not having people fit, but it's natural, and there's the positive because there are opportunities for others.

"Like Alex, for instance. He came to the club, unfortunately got injured, trained so so well and supported the boys incredibly.”

Carrick's side also have injury concerns further up the pitch with Lewis O'Brien (ankle), Riley McGree (foot) and Marcus Forss (thigh) also currently sidelined.

Josh Coburn, who dropped to the bench on Saturday due to a couple of niggles, is back in contention to start on Tuesday.

Sam Greenwood is likely to feature, with the attacking midfielder ineligible in Saturday's game at parent club Leeds.

Fresh defensive blow for Middlesbrough FC ahead of tests against Preston North End and Leeds United