The 2006 All-Star had started the Division 1 final defeat to Cork and was also known to have been performing well — along with Michael Conroy — in training games of late.
However, his right corner-forward position has gone to Alan Freeman, who is fit once more after fully recovering from an ankle injury.
Mortimer is one of three changes from that Croke Park game, with Danny Geraghty replacing Jason Gibbons in midfield and Conroy making way for Jason Doherty. Ballintubber midfielder Geraghty is one of three players making Championship debuts along with Kevin Keane and Lee Keegan in defence.
Leitrim go with 12 of the team that beat London for the Castlebar game. Daniel Beck and Enda Williams in defence and Shane Moran at midfield are in at the expense of James Glancy (St Mary’s), Ciaran Egan and Moran respectively.
Cork have named a relatively experienced side for Sunday’s Munster IHC semi-final clash with Tipperary at Páirc Uí Chaoimh (throw-in 2pm).
The starting 15 features seven players who were involved last year as Cork beat Tipperary before losing to eventual All-Ireland-winners Clare at the provincial semi-final stage.
MAYO (SF v Leitrim): D Clarke; K Keane, G Cafferkey, K Higgins; L Keegan, D Vaughan, C Boyle; B Moran, D Geraghty; K McLoughlin, C O’Connor, A Dillon; A Freeman, A Moran, J Doherty.
LEITRIM (SF v Mayo): C McCann; D Beck, F McMorrow, P Maguire; C Clarke, E Williams, W McKeon; D Sweeney, S Moran; P Brennan, E Mulligan, P McGowan; R Cox, J Glancy, A Croal.
CORK (IH v Tipperary): S Nyhan (Courcey Rovers); B Withers (Banteer), D Rodgers (Brian Dillons), B O’Sullivan (Fermoy); J Jordan (Blarney), V Hurley (Courcey Rovers), S White (Ballygarvan); M O’Sullivan (Tracton), B Lawton (Castlemartyr); O Kelleher (Blackrock), M Sugrue (Bandon), A Mannix (Kilworth); C Casey (Inniscarra), S Harnedy (St Ita’s), D Drake (Carrigaline).