The Japanese has suffered multiple injuries, missing four consecutive games this week for the first time since he joined the Dodgers in 2023.
Ohtani has not pitched in a game since July 3rd. He has battled inflammation and soreness, and experienced injury setbacks after bullpen throwing sessions.
Roberts on Sunday expressed hope that Ohtani could return to the Dodgers' batting lineup as soon as Monday.
But with just three weeks remaining in the regular season, Roberts downplayed the prospect of Ohtani returning to the mound as a full-fledged starter this year.
"Obviously if you're looking at the calendar, how much he's thrown in the last week, I think we can all do the math," said Roberts.
Asked if Ohtani might instead throw just an inning at a time as an opener, Roberts responded: "I think that's unlikely."
Ohtani has played a crucial role as the Dodgers have won back-to-back World Series in the past two seasons, but his pitching role has been limited.
After undergoing two right elbow operations in 2023, Ohtani did not take the mound at all for the Dodgers until last June.
After a rehab-free off-season, this was meant to be the year Ohtani returned as a full-time two-way player, with the Japanese star targeting the Cy Young Award for outstanding pitching.
But that has been derailed by injuries to his left knee, right biceps and neck.
Ohtani's batting form has slumped in recent weeks as he has attempted to return as a pitcher.
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The MLB regular season is now in its final two months as the countdown to the Postseason begins!