Former England fast bowler Angus Fraser believes record-breaking South Africa captain Graeme Smith has technical flaws in his batting that will be exposed.
Records are tumbling Smith's way, but Fraser is not overly impressed
Fraser told BBC Sport he is "surprised" at Smith's incredible run of form with the bat.
Smith hit the highest individual score by a South African with 277 in the first Test at Edgbaston, and followed it up with another double ton at Lord's.
And he is poised to break more batting records before the end of the five-Test series.
But Fraser, now working for Test Match Special, said the 22-year-old is far from the finished article.
"Smith has surprised us all. He is in a magnificent vein of form and he has got a good head on his shoulders so he is going to go down as a top player," he said.
"He is obviously going through a magnificent period of his career, but I don't think he is someone who is going to carry on like this.
"There are technical things in his game that will be exposed at certain stages of his career.
"To think that he is going to carry on scoring the volume of runs that he is, is unrealistic."
But former South African batsman and current batting consultant Graeme Pollock believes Smith will become "one of the
great Test players".
"He is only 22 and he
could probably play on until 35 if he wants to - so how many runs is that?" said Pollock.
"When I took over as batting consultant, I didn't try to change anything. I would have been frightened to meddle with anything. He is playing so well.
"He would climb Mount Everest for South Africa. A sporting hero has been born in our country. Graeme is young, fresh, enthusiastic and committed."