Barnsley FC transfer news: Keeper set for Chelsea return after bittersweet loan spell at Oakwell
The USA international keeper made 14 appearances for the Reds, but suffered a finger injury in November which has sidelined him since.
The 20-year-old's last appearance for the club came in the 2-2 League One draw with Charlton on October 22, with Slonina – despite showing his prowess early on in his time at Oakwell – being dropped from the starting line-up in its aftermath.
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Hide AdReds head coach Darrell Clarke remained effusive in his praise of the young custodian's attitude to being demoted, only for the American to suffer a further blow when he picked up an unfortunate injury.


Meanwhile, the clear-the-air meeting that Clarke held just nine days ago has certainly had the desired effect as far as Barnsley are concerned over Christmas.
After calling his players out following a dishevelled performance in a humiliating 4-0 home reverse against Leyton Orient on December 21, those in red jerseys have delivered a welcome and uplifting response by way of back-to-back away wins at Peterborough United and Bolton Wanderers.
The strong riposte has been given added kudos by the fact that illness and injury niggles have been affecting several players, with several putting their hand up to try and pull Barnsley through in a tough time in their season.
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Hide AdOne or two players have also provided themselves with a lifeline in the process, including Barry Cotter, who is making the most of his return to the fold after being out of the picture just a few weeks ago.
On Cotter, who replaced Georgie Gent on Peterborough, Clarke said: "It was time and minutes and a breather (for Gent). Barry has come in and done well. "Georgie, a 20-year-old, has played a lot of games and football. Barry had a good game and you have to freshen things up.
"Phillo (Adam Phillips) was feeling his calf at the end and it’s making sure we get Max (Watters) through some minutes so he doesn’t break down.
"Fair play to the captain, Luca (Connell), who came back from a virus as well."