Kranjcar played alongside Bale during his three-year stay at Tottenham before leaving for Ukrainian side Dynamo Kiev in the summer.
The Welsh winger has been one of the Premier League's standout performers this season, scoring 16 top-flight goals.
He will look to carry that form onto the international stage when Wales take on Scotland at Hampden Park on Friday before hosting Croatia next Tuesday.
Kranjcar believes Bale is the only player in the world currently on a par with Primera Liga superstars Lionel Messi and Cristiano Ronaldo and knows Croatia must contain him next week.
He told Novi list of his former team-mate: "We don't talk on the telephone or anything like that but I do follow him and his games.
"At this moment Gareth is the only one who can be compared with the two best players in the world - Lionel Messi and Cristiano Ronaldo.
"So we will have to be very careful, we must stop him at any price. He can lead Wales to glory by himself."
Croatia beat Chris Coleman's side 2-0 in Osijek back in October last year and Kranjcar has challenged his side to repeat that performance in Wales.
He added: "If we will play like we did in Osijek then not even Bale will be able to help Wales. But yes, he is really, really dangerous player."