Ward-Prowse was initially named in Gareth Southgate's provisional Euro 2020 group but did not make the final cut for the main squad.
He also missed out on selection for this month's internationals.
Asked whether he felt his midfield partner was overlooked internationally, Romeu told the Daily Echo: “It is tough to say. There is a lot of quality in that team right now and it's hard to get in.
“I would personally think he is one of the players you should always have there, because he gives you different positions, he gives you set-pieces, he gives you so much work-rate - comfortable on the ball.
“The manager will have his decisions – he will know when he picks his players. It's probably not easy to choose among all those players."
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