Summer signing Raya made his debut for the Gunners in Sunday's 1-0 win at Everton as Ramsdale was named as a substitute for the first time in 18 months.
Ramsdale has established himself as one of the better goalkeepers in the Premier League but there remain lingering question marks over his ability to be first-choice for one of Europe's biggest teams, and Hasselbaink believes Mikel Arteta has made his opinion clear.
"They paid a lot for Raya and I think he’s their No.1 and eventually he was going to play, I think today is the first day that he’ll be a regular," he told Sky Sports.
"I don’t see goalkeepers getting minutes here and there, they need rhythm, they need to stay in that momentum.
"Raya is a very good goalkeeper and Aaron is as well, two big goalkeepers you want in your team. It’s hard and a difficult decision but I think we’ll see Raya in Arsenal’s team for a little while."
Raya has joined on a season-long with an option to make the move permanent for around £30million, with both Arsenal and Brentford expecting the clause to be triggered.
Theo Walcott, though, does not believe it is the end of the road for Ramsdale, adding: "I think it’s a really interesting point you say about the fixture pile-up but I’m a big fan of Aaron.
"I think you got to look at England’s perspective as well. It will be interesting to see how he reacts, he’s had to deal with a couple of relegations but this is something else.
"He’s at a very team, he’s got No.1 on his shirt there and now he’s got a keeper challenging him. They’re going to buy him in time and it’s very interesting. I’m sure he can deal with it."