Tomori fell down the pecking order at Chelsea in the first half of this past season, struggling for regular game time.
He went on loan in the winter transfer window, signing for AC Milan on a short term deal.
Tomori made an excellent impression with Milan in Serie A and may even secure a permanent move to the Italian giants this summer.
"Honestly, I am a bit surprised because from their choice of centre halves, they all seem to have the same characteristics," Rebic, who will play against England for Croatia in the group stages on Sunday.
"Fik is aggressive and fast. We talked and he said that he didn't believe he was going to be called up.
"So I'm a bit surprised."