Thomas joined Rovers on loan in the close season on a season-long loan from the Oakwell club, but was not involved in the match-day squad for their weekend League Two game with Crawley Town.
Gloucestershire-born Thomas, who joined in the summer of 2019, has struggled to establish himself in the Reds' line-up during his time with the club.
The 22-year-old, whose Oakwell deal runs until June, 2023, was allowed on loan to League One side Ipswich Town in January.
Thomas spoke about losing confidence during the season with Barnsley and being desperate to get out and play games at Ipswich.
The wingman played just five times for the Portman Road side, with the last appearance being in mid-February.
He later revealed that he needed to take a break from football for the benefit of his mental and physical health.
On the current situation with Thomas, Barton told Bristol Live: "Luke Thomas, we’ve decided to get him fit, to take him out of the matchday squad for the last couple of games, because we feel we can get more physical work into him.
"He missed pre-season, didn’t really tap in until the last couple of weeks of it. He’s not played since February last year. He’s had a few mad moments both on and off the pitch in between that.
"He needs to get himself as fit as he can to impact games, so we’re having a bit of a mini pre-season with Tommo at the minute and he’ll probably miss next Saturday but will possibly be back with the group the Saturday after.
"He’s got work to do. You can’t turn form and fitness on like a light switch, you’ve got to do the hard yards and for whatever reason, he’s been caught in between football clubs.
"He’s been getting loaned out when it’s maybe not the best thing for him. He’s had some off the field stuff that he’s had to resolve and he’s a young man who’s got to work incredibly hard to get himself back to the level that no doubt earned him the move to Barnsley."