F1 Grand Prix Of Singapore - Source: Getty
Former F1 team boss Guenther Steiner issued a brutal verdict regarding Daniel Ricciardo getting axed from RB, saying that this was just the ruthless nature of F1. Red Bull brought the Australian back from the sidelines after an impressive tire test performance, where his lap times were competitive compared to what Max Verstappen had done during the race weekend.
Daniel Ricciardo was placed at RB this season to see how he would perform alongside Yuki Tsunoda. If his performances were up to the mark, Red Bull would have considered the Australian one of the primary options if Sergio Perez was not up to the mark.
18 races into the season, however, Red Bull decided that the Daniel Ricciardo experiment had not worked. Ricciardo couldn't put together a compelling enough case where he beat Yuki Tsunoda consistently and performed at a high enough level to get the promotion.

