Saints boss Steve Lomas is banished to the stand, while defenders Dave Mackay, Frazer Wright and Steven Anderson are suspended along with midfielder Chris Millar.
"They do have defensive problems, because they have four players suspended for the game," McGlynn said.
"From the midfield forward they've still got a lot of attacking options, so we have to make sure that we don't think just because St Johnstone have got a few suspensions it's just a matter of turning up.
"That can be costly. We've got to make sure we have the right attitude.
"We won against Aberdeen last week and we look to go up to Perth and play as well if not better and be as committed, if not more, and win that football match."