Indeed, he was one of their best players that played consistently with them, so missing him against one of the best teams in the NBA is really huge.

Here's his status, https://www.foxsports.com/nba/josh-giddey-player

He exit during the game with LA Clippers due to twisted ankle, but there was no report of a fracture or whatsoever, so I'm expecting that it's just a sprained ankle, he might miss few games but he'll come back for sure. I'm sure OKC won't struggle hard even without him, they are not like the Memphis though, but against strong teams, they will miss the service of Giddy. Hope he'll get back soon.