Roy is in contention to be promoted to the top of the order to partner county team-mate Rory Burns for this year's Ashes series against Australia with Keaton Jennings' place under threat.
The 28-year-old has been a star of England's one-day team and could make his Test debut against Ireland in July in an audition for the summer's main event.
"Jason is opening in one-day international cricket. Twenty20 and Test cricket are miles apart, but in the first 10 or 15 overs of 50-over cricket you still have to respect that new ball," Stewart said.
"I don't see it as a big issue for him and he'd cope with the stepping stone up to Test cricket.
"The Australia attack is a challenging attack, but Jason's method is a solid one. He's a good stroke player and a good hitter of the ball, but he can defend well too, which you have to be able to do.
"Jason is unlikely to be fit for the Essex game with this (hamstring) problem. We're hoping he is, but it's unlikely.
"His first red-ball innings could therefore be against Ireland in a Test match, assuming he has a good World Cup."
Surrey are the reigning Specsavers County Championship champions and Stewart insists they will have to step up a gear if they are to retain their crown.
"The message we've given the boys is that if we're as good as last year then that's OK, but we've got to be better," Stewart said.
"Previously we were the hunters but now we're the hunted. Everyone will be trying to catch us up through hard work and by trying to improve, so we want to keep that gap.
"That's easier said than done because of a lot of other counties have strengthened. Notts will have Stuart Broad available for a decent amount before the Ashes starts.
"Essex have Alastair Cook - having him available all season is like having a world-class signing so they'll be stronger again.
"We brought in Liam Plunkett and Jordan Clark. We're expecting England call-ups and want England call-ups. Therefore we want a squad where people are available.
"If you look at our squad, then everyone is good enough to play in the first team.
"There will be injuries and loss of form and we're trying to have enough bowling stock so that we can rest and rotate.
"We don't want to bowl people into the ground, which may create injuries."
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