The Reds did not add to their squad on transfer deadline day last Friday, despite efforts to sign a centre-back on loan.
They are still hoping to recruit in that position as they can sign free agents after the window. One name discussed at Oakwell has been Sebastian Prodl, a 32-year-old with 73 caps for Austria who was released by Premier League Watford last week.
He played just five games for the Hornets in the last two seasons.
Due to Bambo Diaby’s suspension while the FA investigates his alleged failed drugs test, Barnsley’s only available centre-backs are January signing Michael Sollbauer, Mads Andersen and Aapo Halme, who Struber has been using in central midfield.
Head coach Gerhard Struber said: “It’s a priority we can pick up a good player in defence, but we need the right player, and when we’re not 100 per cent convinced this is the right player it’s better we don’t do it.
“When we find a player it’s important he gives me a good feeling and he has a good feeling with us. But it’s not so easy.
“I trust my boys and believe in them, but it’s no surprise that one or two players with high quality are necessary for the bigger task of staying in the league.”
Full-backs Dani Pinillos and Dimitri Cavare, along with winger Mamadou Thiam, remained at the club despite being out of Struber’s first team squad.
They were all understood to have offers to leave but rejected them, with Thiam turning down the chance to reunite with former head coach Daniel Stendel at Hearts.
Struber said: “They’re not involved in my plans for the next few months. We had a clear exchange and I spoke very clearly with the boys.
“Every player has a history and a strength. Connecting that with my ideas can be very difficult. This is a normal process and I think the players know what the situation is.
“I understand it’s not a simple situation for the players. They have no game time and when they look in the future it’s not so easy to get it in the next few months.”
All three will continue to train with the first team, despite Cavare posting a picture on Twitter of him seemingly training with the under 23s.
Pinillos tweeted: “Being a better or worse football player is secondary, first of all we are persons and I think everyone should be treated with the same respect. Too bad there are people who don’t seem to see it that way.”
Asked about that tweet later in the day, Struber said he had not seen it but would speak to Pinillos.
On Thursday, he said: “They know they’re in a difficult situation but they’re not surprised. They will stay here, they will work with us, and it’s not a situation that makes me happy.”
Asked to sum up the window, in which he recruited three of his former players from Austrian football, Struber said: “We bring good players into the club and, in the end, we were a little unlucky with one or other players. Now we have this squad and we have to work hard with them.
“It was a disappointing moment when we could not find the right defender in the window.”
The Reds brought in two players for their under 23s squad on deadline day, Scottish youth international Ethan Erhahon, 18, and 20-year-old centre-back Ali Omar.