A 2-0 victory over the struggling Tykes, which came courtesy of goals from on-loan duo Nicky Maynard and Martyn Waghorn, lifted Rosler's men up to seventh in the Sky Bet Championship table, four points away from the play-off zone with a game in hand.
However, the win was overshadowed by the sight of Watson, the figurehead of last season's triumph over Manchester City at Wembley in May, leaving the pitch on a stretcher amid fears of a second broken leg in 15 months after a full-blooded first-half collision with Barnsley's Martin Woods.
Rosler could only confirm Watson, who left the DW Stadium in an ambulance, was in hospital and would not be drawn on whether the central midfielder would miss the holders' mouth-watering quarter-final tie against City, or potentially the rest of his Wigan career with his contract due up in the summer.
"The sore note is now Ben Watson; we don't know (how serious it is) at the moment, it's too early to say," the German said.
"I don't want to speculate, the worst thing is speculation. He's in hospital now, we will find out later on or on Wednesday morning.
"We could lose him for three days or we could lose him for three months. We must be clear what he has, how long he will be out, at this moment in time I don't know.
"I've seen many players going to hospital to have an X-ray, to have a scan, that does not necessarily mean it is something serious.
"We hope it's not. Obviously it didn't look good but people have been carried off on a stretcher who played the next game."
Watson's injury caused a lengthy stoppage and clearly shook some of his team-mates at the time but, to their credit, they quickly focused their concentration back on the task in hand with Maynard and Waghorn netting before the interval.
Rosler continued: "These games against the so-called underdogs are the most difficult ones.
"The players have been tremendous in their application, they didn't get carried away or lose their focus with Ben's injury - sometimes it's difficult but we kept it.
"The left-hand side combination football - (Jean) Beausejour, (James) McClean, Chris McCann, Nicky Maynard was excellent, breathtaking. Both goals came from that side, I didn't feel they could cope with that.
"Second half we were running out of fuel, we didn't attack in the manner I'd like, but I understand that because of our match programme."
- Sports & Recreation
- Nicky Maynard
- Martyn Waghorn
- Ben Watson