Complex sentence: Mackay, however, reportedly had a poor relationship with George Burley, the manager who led Derby to a play-off place in 2004--05, with rumours of disagreements and meddling in team affairs by Mackay.
Split into simpler sentences: Mackay, however, reportedly had a poor relationship with George Burley, the manager who led Derby to a play-off place in 2004--05. There were rumours of disagreements and meddling in team affairs by Mackay.