The Garrycastle player damaged knee ligaments towards the end of Saturday’s All-Ireland qualifier against Tipperary and the initial diagnosis is that he will be out for 12 weeks.
“Losing Dessie is obviously a big blow for us,” said selector Jack Cooney.
“Everyone knows what an important player he’s been for Westmeath the last few years. It’s been a tough year for us with injuries and that’s hard for a county like Westmeath that has less resources than a lot of others.
“I was very disappointed for Paul Conway who broke his leg as well. He had just come back from an injury and we were looking forward to seeing him play again with a game under his belt but that won’t happen now.”
Galway have drafted in U21 full-back Finian Hanley ahead of the Connacht SFC final against Mayo on July 10.
The towering Salthill Knocknacarra clubman was outstanding for the county side which captured the All-Ireland U21 title last month.
Senior manager Peter Ford brought Hanley into the squad after a far from convincing display by his full-back line in their 1-11 to 1-8 semi-final win over Leitrim.
Galway have struggled to fill the full-back position after long-serving Gary Fahey decided to retire at the end of last season.
Corofin’s Kieran Fitzgerald moved from the corner to the edge of the square this season but looked vulnerable against Leitrim and may revert to his corner position again.
Hanley’s addition to the squad could be crucial, with clubmates Val Feeney and Niall Coyne both doubtful after being injured in Carna-Caiseal’s win over Tuam Stars on Sunday.
Manager Eamon Coleman won’t name a Cavan team for the Ulster SFC semi-final replay until later in the week in order to allow players recover from bumps and bruises. He will however be without Paul Brady who received a straight red card last Sunday.
SATURDAY: Nicky Rackard Cup: (3.30 unless stated) Group 3A, Round 2 Fermanagh v Sligo, Enniskillen, (J. O’Rourke, Monaghan).
Donegal v Tyrone, Letterkenny (M. Mulholland, Derry).
Group 3B Round 2: Cavan v Louth, Clones, 3.45, (J. Devlin, Tyrone).
Leitrim v Armagh, Carrick-on-Shannon (T. Mahon, Fermanagh).
Group 3C, Round 2London v Monaghan, Ruislip, 4.30, (J. Owens, Wexford).
Warwickshire v Longford, Birmingham, 5.30, (D. Connolly, Kilkenny).
Christy Ring Cup: Group 2A Round 3 Derry v Meath, Ballinascreen (P. Greene, Galway).
Down v Roscommon, Ballycran, (E. Morris (Dublin).
Group 2B Round 3:Kildare v Mayo, Naas (JA Gibben, Down).
All-Ireland Hurling Qualifier: Round 1, Roinn A Antrim v Limerick, Casement Park, 2.30pm, (J. McGrath, Westmeath).
Bank of Ireland Ulster SFC semi-final Replay Tyrone v Cavan, Clones, 5.30pm, (P. Russell, Tipperary).
SUNDAY: Bank of Ireland Ulster SFC Semi-final Derry v Armagh, Casement Park, 2.15, (M. Monahan, Kildare).
All-Ireland Football Qualifier: Round 1 Wicklow v Donegal, Aughrim, 3pm, (G. Ó Conámha, Galway).
Guinness Munster SHC Final Cork v Tipperary, Pairc Uí Chaoimh, 4pm, (B. Kelly, Westmeath).