Complex sentence: He (John) originally came to Scotland for a trial with Kilmarnock but their manager, at that time, Jim Jefferies said that he was an excellent player but was not quite what he was looking for at that time.
Split into simpler sentences: He (John) originally came to Scotland for a trial with Kilmarnock. Then manager Jim Jefferies said that he was an excellent player but was not quite what he was looking for at that time.