Saliba, 18, signed a five-year contract but will continue his development with the Ligue 1 club next season, before joining Arsenal in the summer of 2020.

Spanish international Ceballos has joined on a season-long deal.

The 22-year-old has played 56 times for Madrid since joining from Real Betis.

Of the loan signing, Gunners head coach Unai Emery said: "We're excited to see Dani join us. He is a talented player with big technical ability, creativity and precision."

Ceballos, capped six times by his country, will wear the number eight shirt this season and could make his debut against Lyon in the Emirates Cup on Sunday.

The signing of Saliba is the culmination of interest dating back to autumn 2018 and comes despite late interest from Tottenham.

The France youth international's return to Saint-Etienne next season was a non-negotiable condition of the deal.

"We're delighted William is joining us," Emery said.

"Many teams wanted him but he decided he wanted to come to us and be part of our future.

"He will stay in France next season for more experience and then we look forward to him joining our group."