The experienced former Chelsea goalkeeper started the season as Unai Emerys first choice between the posts but lost this place after he suffered an injury against Watford in September.
Following an impressive start, Leno has made a succession of costly mistakes and was powerless to prevent Arsenal from suffering their heaviest defeat under Arsene Wengers successor at Anfield on Saturday.
Arsenal have struggled to find a goalkeeper worthy of replacing club legends David Seaman and Jens Lehmann, and Keown fears Leno doesnt fit the bill either.
Leno didnt even make the German squad, said Keown. Is he better than Petr Cech? No I dont think so, but Petr Cech hasnt played since September.
Leno, meanwhile, thought Arsenals 5-1 defeat at Anfield was unlucky, saying: We conceded too many unlucky goals.
The first goal was so unlucky because there was no danger.
Some seconds later, the ball was in our goal. In the first half, we made too many mistakes & Liverpool are a team who can score with every chance. It was an unlucky day for us.
I dont think that was the difference today. Of course we conceded five goals but I think we as a team made too many mistakes. We have enough quality, even when somebody is injured. Today injuries were not the problem.