The 18-year-old Japanese midfielder has been training with Dortmund's senior squad throughout pre-season after arriving on a season-long loan from Gamba Osaka in July.
Although the current strategy is for him to feature primarily for the club's U23 side, which plays in Germany's fourth tier, Kovac stressed that a route into the first team remains open.
Yamamoto has already attracted attention by finding the net in Dortmund's pre-season victory over Rot-Weiss Oberhausen. His promising displays have inevitably sparked comparisons with fellow Japanese midfielder Shinji Kagawa, who became one of the Bundesliga's greatest Japanese success stories after joining Dortmund in 2010.
Under Jurgen Klopp, Kagawa rapidly established himself as a key figure and helped the club secure back-to-back Bundesliga crowns before earning a move to Manchester United.
While acknowledging Yamamoto's considerable talent, Kovac emphasised that the youngster's progress must be handled carefully rather than rushed.
"I saw him for the first time [in that game]," Kovac said.
"He had some good moments. I saw real potential, and that's positive for us. We'll be keeping an eye on him."
Dortmund's preparations for the new campaign will continue with a tour of Japan from 26 July to 2 August. The Bundesliga side will then head to London, where they are scheduled to meet reigning Premier League champions Arsenal in another pre-season fixture.