As it was announced during his presentation, Martin Ødegaard is training with Real Madrid's first team. The Norwegian midfielder will be a Real Madrid Castilla player though, so he should not feature in a match with Cristiano Ronaldo and co. unless Ancelotti decides to use him, just like any other Castilla player.
Ødegaard arrived in Madrid with a small problem on his thumb, but it seems that he has recovered properly from this injury and might as well be available for Castilla's weekend match.
There are high expectations about Ødegaard, but the club will be patient to allow him develop as a complete player. That way, he will complete the rest of the season with Castilla -- who are trying to achieve promotion to Segunda -- and then have his situation reassessed after completing the 2015-2016 pre-season with the first team. This was just the first of many training sessions that Ødegaard will complete with Real's first team.