"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.
"He's in hospital now. We will find out later on or Wednesday morning. I don't want to speculate, the worst thing is speculation.
"We could lose him for three days or we could lose him for three months. 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."
Rosler's side are now unbeaten in their last six home league matches and moved to within one place of the top six, with a game in hand on sixth-placed Reading.
The hosts reacted well to a four-minute delay caused by Watson's injury and took the lead when Maynard converted from close range from Beausejour's left-wing cross.
Waghorn's maiden goal for the Latics, from McClean's cross, doubled the lead before the break to leave Barnsley second from bottom in the Championship.
Wigan boss Uwe Rosler:
"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 - Beausejour, McClean, Chris McCann, Nicky Maynard was excellent, breathtaking. Both goals came from that side, I didn't feel they could cope with that."
Barnsley manager Danny Wilson:
"They're a very good side and they'll be challenging for (promotion to) the Premier League this year.
"The top six is their target and when you see them play in full flow, you can see them being there.
"We gave it everything in the second half, which pleased me. It wasn't there but we move on."
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