Grobbelaar is of the opinion that the defensive problems experienced by the Reds last season have not been rectified, while he also suggested that Mignolet is the main culprit for their poor defensive record.
In an interview with BBC Sport, Grobbelaar said: “Any team that lets in 50 goals should never be in second position in the first place.
“That was masked and brushed over by the brilliance of Suarez and [Daniel] Sturridge scoring so many goals.
“You’ve got to shore up at the back, get yourself someone in goal that can only let in 30 goals a season, or less than 30 goals a season.”
When asked if he still felt that Mignolet wasn’t good enough, Grobbelaar said: “I’ve always said that. I’ve said that he doesn’t command his area.
“I have likened him worse than Dracula, because at least Dracula comes out of his coffin now and then. He seems to stay on his line and that’s it.
“That whole area – not the six-yard area, the 18-yard area – is the goalkeeper’s, and in this day and age, in modern goalkeeping, if you come out and catch the ball and you get smacked you are going to get the foul.
“It’s not rocket science, and he is a big lad. As soon as that ball is in the air – get out, come for it.
“You’re going to get a lot more fouls for you and less are going to go in the back of the net.”
Mignolet joined Liverpool from Premier League rivals Sunderland in 2013 after a reported fee of £9m was agreed between the two clubs.
To date, the Belgium international has made 57 appearances in all competitions for the Reds.