O'Connor has been sidelined with a back injury and though not considered for selection yet, his return to training is a welcome relief to the Connacht management, with the back row ranks still missing injured captain John Muldoon and recent signing Ezra Taylor.
Griffin (hand) and Tuohy (back) also returned to training and will look for inclusion in the coming weeks.
Gavin Duffy (back), Frank Murphy (foot), Fionn Carr (foot) and Jamie Hagan (back) all pulled up out of training on Tuesday after carrying knocks from last Friday's win over Glasgow Warriors. Their progress will be monitored throughout the week to assess their availability for the weekend's interprovincial derby.
Meanwhile, Iarnród Eireann have announce that special train arrangements will be in place to cater for rugby supporters who wish to travel from Athlone, Ballinasloe, and Athenry to Galway for the Connacht v Ulster clash on Saturday.
Passengers will be able to avail of regular trains departing Athlone at 4.04pm, 5.04pm and 6.02pm, all of which will arrive at Ceannt Station in time for the game.
A return train will depart Galway at 10.15pm, returning to Athlone and serving Athenry, Attymon, Woodlawn and Ballinasloe.
The return fare, which should be purchased on the day from Station Ticket Offices, is an attractive €10.
CONNACHT Squad (v Ulster) - Backs (12): Cillian Willis, Frank Murphy, Miah Nikora, Ian Keatley, Fionn Carr, Keith Matthews, Niva Ta'auso, Tiernan O'Halloran, Aidan Wynne, Troy Nathan, Gavin Duffy, Darragh Fanning.
Forwards (14): Ronan Loughney, Brett Wilkinson, Sean Cronin, Adrian Flavin, Rob Sweeney, Jamie Hagan, Andrew Browne, Dave Nolan, Michael Swift, Bernie Upton, Michael McCarthy, Ray Ofisa, Mike McComish, Shane Conneely.
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