Complex sentence: Manager Claudio Ranieri aimed to qualify for the UEFA Champions League, but resigned in February following poor results, and his successor Radomir Antić's stewardship saw the club relegated into the Segunda División.
Split into simpler sentences: Manager Claudio Ranieri aimed to qualify for the Champions League, but resigned in February following poor results. The club's league form did not improve following Ranieri's departure, and his successor Radomir Antić failed to prevent the club from being relegated into the Segunda División.