Number 8 Nick Williams played the full match in Neath, his first outing for Munster since injuring a knee at the end of September.
Meanwhile, hooker Damien Varley's last appearance was off the bench in the Heineken Cup game against Northampton Saints in mid-January. He damaged a pectoral muscle in action for Garryowen in early February.
Gleeson injured a hamstring in that Neath game and is expected to be sidelined for up to three weeks.
Barry Murphy continues to recover from an ankle injury and he was in UL yesterday (Tuesday), sitting out training alongside Ian Dowling who was also nursing an ankle injury but is expected to feature against the Dragons.
Niall Ronan (bicep) is close to a return to action, while prop Dave Ryan had resumed playing after a shoulder injury - only to succumb to hamstring trouble in a club game that is expected to rule him out for a week or two.
Ireland lock Donnacha Ryan had a shoulder operation yesterday and will be out for the immediate future.
Prop Darragh Hurley has resumed light training but is not expected to be back in action for some weeks yet and it is unlikely that either Denis Leamy or Felix Jones will play again this season.