Complex sentence: On 20 January 2014, Campbell joined Championship side Millwall on loan for the remainder of the 2013--14 season, uniting him with manager Ian Holloway, whom Campbell has previously played for at Blackpool.
Split into simpler sentences: On 20 January 2014, Campbell joined Championship side Millwall on loan for the remainder of the 2013--14 season. The loan move reunited Campbell with manager Ian Holloway, whom Campbell has previously played for at Blackpool.