Leno was one of five summer signings completed by new boss Unai Emery as he bids to rebuild Arsenal in the post-Wenger era.
However, Keown has doubts about the new goalkeeper citing missing out on the recent German national team squad and his shot-stopping ability as major stumbling blocks.
“If you look at the statistics for goalkeepers in Europe, Leno excels in his distribution but is not the best when it comes to the shots he is expected to stop,” he said in his Daily Mail column.
“The German was not in their World Cup squad and hasn’t been called up for this international break.
“How good is he? We’re not too sure yet.”
Leno joined Arsenal from Leverkusen in June this year for a reported £22.5m after having spent seven years at the club.
The 26-year-old started his professional career at VfB Stuttgart II where he made 57 appearances before moving to Leverkusen in 2011 for a reported £9m.
Leno appeared 304 times in all competitions for Leverkusen and appeared six times for his country before moving to England.
Leno missed out on last weeks Germany squad; the first Germany squad since they exited the summers’ World Cup in Russia at the group stage for the first time in their history.
He also was not part of the squad that travelled to Russia, and Keown sees this lack of international pedigree as a reason to doubt the abilities of Leno.
As he mentions, Leno is known for his distribution which is massively sought-after in modern goalkeepers, but he infers there is little point in having this attribute if you struggle with the more essential goalkeeping skills.
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