Blues fans' needn't fear that their side may be about to snap up the singer, however, with Horan merely using the facilities to step up his fitness after suffering an injury to his knee recently.
Jose Mourinho, whose daughter is reportedly a massive fan of the band, has allowed the 1D star to receive treatment and he was snapped alongside the likes of first-team players such as John Terry and Fernando Torres during his visit.
Last year Horan and the rest of the group joined Mourinho in a private training session at Real Madrid, where they came up against the La Liga outfit's all-star cast after being invited along to Ciudad Real Madrid.
Band-mate Tomlinson made his debut for Doncaster's reserve side last month.
image: © bensutherland