Chelsea have completed a loan deal with Atletico Madrid for Saul Niguez with the deal containing an option to buy next summer.

The deal was thrown into doubt as the transfer had not been confirmed by either club before the midnight CET deadline.

Local media said the delay was caused by a problem with LaLiga's transfer registration system, however, and the documentation had been correctly submitted in time.

"We welcome Saul to the Club and believe he completes our squad as we compete for honours in five different competitions this season," Chelsea director Marina Granovskaia said.

Chelsea are in talks with Atletico Madrid on a season-long loan of Saul Niguez with an option to sign a permanent deal.

Manchester United have also remain interested in Saul but have not been able to reach an agreement with Atleti on a fee.

Saul, 26, has started both of Atletico's league games so far this season but has lost his status as a key player for coach Diego Simeone over the last year.