Federer struggled in his second round match against Radu Albot, needing three sets to get over the line.
And the 37-year-old says he knows Krajinovic will provide a challenge.
“I practised with him in Australia and he played very well against me there, and I like his game,” he said.
“He takes the ball early, he can keep the ball in play, he can take on the backhand down the line and he is very steady.
“With his talent, it makes him a dangerous player plus he has beaten Stan [Wawrinka] today so I’m sure he’s ready.”
18:00: An update from the Miami Open – “WEATHER ALERT. NO PLAY BEFORE 2:15 PM
We’ll keep you updated as we learn more.”
For those in the UK, it means a further update will come at around 18:15 GMT.
17:40: It is currently raining in Miami which means there is a stoppage in play. When the rain came, Kvitova was leading Garcia 6-3 5-2.
17:30: Hello and welcome to coverage of Roger Federer’s clash with Filip Krajinovic at the Miami Open.
The match will get underway once the clash between Caroline Garcia and Petra Kvitova concludes.