According to the Daily Mail, both clubs are interested in securing the 21-year-old, who currently plays for Croatian side Slaven Belupo.
The newspaper adds that Rangers boss Steven Gerrard, who has earmarked the youngster as a priority target, could complete the signing for around £2m.
"There was a representative from Glasgow Rangers in Croatia three weeks ago," a spokesman for Katic's agent, Mladen Kliskinic, told the news outlet. "There is another story that Spartak Moscow are also interested. Mladen Kliskinic has booked a flight to go and speak to them on Tuesday.
"But we are waiting for Slaven Belupo to confirm they've accepted a concrete offer. Until that happens nothing can be finalised."
Katic, a former Croatia Under-21 international, earned his first senior cap for his country last year.