Bundee Aki's absence from the Connacht side to face Ulster at the Aviva Stadium tomorrow will be a major concern to Andy Farrell who is already down one Lions centre for the November internationals.
However, while the western province are "monitoring" the midfielder's knee after his first game of the season against Munster last week, it is expected that he will be fit enough to train with Ireland when they get together next week.
Once he comes through those sessions, Aki is expected to start the games against Japan and his native New Zealand alongside Garry Ringrose next month, with Stuart McCloskey and Ciarán Frawley the other inside centres in the squad.
In his absence, Andy Friend will pair Tom Daly and Sammy Arnold in midfield for tomorrow's second successive interprovincial clash after last week's defeat to Munster.
Kieran Marmion and Eoghan Masterson also come into the side, with Caolin Blade and the injured Cian Prendergast missing out. Conor Fitzgerald returns to the bench where he'll cover Jack Carty.
There was good news for Farrell in the return of Iain Henderson from his injury. The Lions second-row will start his first game of the season as captain.
Henderson is expected to start the Japan game if he comes through unscathed tomorrow, while McCloskey and Robert Baloucoune are also back in action after being named in the Ireland squad despite therir injury issues.
Eric O'Sullivan also returns to Dan McFarland's side who are looking to make it five wins from five at the start of the campaign.
Munster have another returning Lion in their ranks, as Conor Murray is named on the bench for their trip to Swansea to face Ospreys.
Damian de Allende is also on the bench as he takes a hiatus from Springbok duty to line out for his club for the first time this season.
Tadhg Beirne starts at blindside flanker, with Peter O'Mahony at openside and Jack O'Donoghue at No 8 in a fascinating back-row. Gavin Coombes and John Hodnett can make an impact off the bench.
Jack Crowley becomes Munster's third starting out-half of the campaign, wearing the No 10 shirt for the first time in his career with Ben Healy on the bench.
Ospreys are the top ranked Welsh side so far in the United Rugby Championship and Irish second-row Jack Regan is set for his club debut off the bench.
CONNACHT - T O'Halloran; J Porch, S Arnold, T Daly, M Hansen; J Carty (capt), K Marmion; M Burke, D Heffernan, F Bealham; N Murray, U Dillane; E Masterson, C Oliver, P Boyle. Reps: S Delahunt, J Duggan, J Aungier, O Dowling, J Butler, C Blade, C Fitzgerald, D Kilgallen.
ULSTER - E McIlroy; R Baloucoune, J Hume, S McCloskey, C Gilroy; B Burns, N Doak; E O'Sullivan, R Herring, T O'Toole; A O'Connor, I Henderson (capt); M Rea, N Timoney, D McCann. Reps: B Roberts, A Warwick, R Kane, K Treadwell, G Jones, D Shanahan, M Lowry, B Moxham.
Connacht v Ulster, Aviva Stadium, tomorrow, 5.15; TG4, Premier Sport
OSPREYS - M Nagy; A Cuthbert, O Watkin, K Williams, M Protheroe; S Myler, R Webb (capt); N Smith, E Taione, T Botha; B Davies, R Davies; S Cross, J Morgan, E Roots. Reps: I Phillips, G Thomas, R Henry, J Regan, M Morris, R Morgan-Williams, J Hawkins, D Evans.
MUNSTER - M Gallagher; A Conway, L Coombes, D Goggin, S Daly; J Crowley, C Casey; J Loughman, N Scannell, J Ryan; J Kleyn, F Wycherley; T Beirne, P O'Mahony (capt), J O'Donoghue. Reps: K O'Byrne, J Wycherley, K Knox, G Coombes, J Hodnett, C Murray, B Healy, D de Allende.
Ospreys v Munster, Swansea.com Stadium, tomorrow, 7.35; RTÉ2, Premier Sport