Sounds like Matt Hughes is already training for his upcoming fight against Diego Sanchez ... at the Trails End Bar and Grill in Taylor Springs, IL.

The former UFC welterweight champion is under investigation for an April 23 altercation that left a female patron with a broken nose, according to the bloodhounds at TMZ:

According to a source who was inside the bar, Hughes got into an argument with a male bar patron ... which led to some forceful shoving.

Sources tell us ... the woman is alleging Hughes pushed the other man into her ... and she suffered a broken nose in the collision.

No arrests have been made and no charges have been filed at this time.

After Thiago Alves booted him from the 170-pound title hunt back in 2008, Hughes (45-8) managed to string together three consecutive wins before B.J. Penn pasted him at the 21-second mark of their rubber match at the UFC 123: "Rampage vs. Machida" event last November.

Hughes, who turns 38 in October, has been enjoying some downtime after a busy 2010 fight campaign that saw the flinty farmboy compile a 2-1 record with wins over Renzo Gracie (UFC 112) and Ricardo Almeida (UFC 117) before the aforementioned drubbing in his Hawaiian trilogy.

The fight against Sanchez is rumored for Sept. 24 at the Pepsi Center in Denver, Colorado, however nothing is official at this time.

Stay tuned to MMAmania.com for more updates to this breaking story as they become available.