"Aaron not in goal really shocked me if I’m honest. I find it hard to understand," he said on the Seaman Says podcast.
"I still can’t get my head around if they’re going to be swapping and chopping and changing the goalkeeper. I don’t like that from what it does at the back because the players have to get used to two different goalkeepers.
"But I think the bigger question is: Who plays Wednesday [against PSV] because it’s UEFA Champions League and neither of them have played in it. I think that’ll be a telling point as to who’s going to continue.
"David Raya’s got loads of experience and is good quality. He’s going to want to play, he’s going to need to play. You can’t keep a goalkeeper like that as a number two for a long period because if Aaron gets injured David needs to be up to speed.
"That’s the only thing that I can think. There’s a lot to look at going forward as to why he’s done this but at the moment for me it’s really hard to work out. I’ve never seen this before."
Seaman also added that he thinks Ramsdale will be ‘disappointed’ by Arteta’s decision and doesn’t see how Arteta will be able to effectively rotate the two shot-stoppers, saying: ‘It’s weird because Aaron’s not played badly at all.
‘He’s played well and he’s coming off the back of a win with England up in Scotland in which he was brilliant out from the back. He didn’t have many shots to save but is coming off a high and then to receive the news that he’s not playing must have been quite disappointing for him.
"This is his third season, he’s established and you’re expecting to carry on as number one until he has a couple of dodgy games but I never saw this coming. It’ll be tough for him because he’s only 25 don’t forget.
"It depends on what happens next. Is he still gonna chop and change when both of them are playing really well? Or is he going to wait for one to make a mistake? But then that’s a little bit unfair because Aaron’s not made any mistakes and he’s left him out."
Arteta handed David Raya a surprise start against Everton on Sunday. After the game, the manager said he would use both goalkeepers.
Arsenal host PSV in the Champions League on Wednesday before the North London Derby this weekend.