The Ivorian has failed to live up to his price-tag after becoming Arsenal's most expensive player last summer.
But Robson thinks it is too early to judge Pepe, believing Arteta must find his best position.
"Slightly too early [to call him a flop]," Robson told ESPN.
"He hasn't been a great success this season so far. He's had one or two good games, couple of good free-kicks. I'm not sure they've found the right position for him.
"They've tried him on the right wing where he spent most of his time in France. Then they tried to play him upfront for a couple of games.
"Yet he's got pace, he can do lots of things. At the moment they haven't got the best out of him, he doesn't look a confident player. So he's a flop at the moment but I think he can get better next year under [Mikel] Arteta."