Estonia winger Sander Puri could make his St Mirren debut after signing a short-term deal, with manager Danny Lennon vowing to consider him for the final. Lennon is further boosted by the return of defender Lee Mair (stomach) and captain Jim Goodwin (calf).
Hearts right-back Fraser Mullen is out after suffering a broken foot in the Edinburgh derby - but there are options to replace him as Darren Barr returns from suspension and Dylan McGowan is winning his battle to overcome an ankle injury. Defenders Danny Grainger (knee), Jamie Hamill (knee) and Marius Zaliukas (ankle) plus midfielders Callum Patterson (foot) and Scott Robinson (knee) are out.
Top scorers (all competitions): Steven Thompson (St Mirren) 14;
John Sutton (Hearts) 7
Referee: Craig Thomson ( Scotland)