The Dutchman was impressed with the young striker’s performance in Hearts’ victory over Medeama in the Ghana Premier League.
The Phobians ended a run of four matches without a win by beating Medeama 3-1 at the Accra Sports Stadium on Wednesday.
Issah scored a double in the important victory but was substituted early in the game after complaining about a stomach issue.
Addressing the media in the aftermath of the game, Koopman praised Issah’s performance and compared him to Romario.
"It was a pity that Hamza was sick at half-time. He had a lot of problems with his stomach, every time [he went to] the toilet," the Hearts coach said.
"I asked 'Where is Hamza?' Again, he was on the toilet so I needed to change him. But you see the quality of Hamza, he has something from Romario, low on the ground, [and] turns very fast. I like him very much."
Meanwhile, Hearts have moved up to 13th on the Ghana Premier League table following their win over Medeama.