Arsenal shore up defence with Tierney, Luiz deals

Scotland international Tierney had been a target all summer for the Gunners and agreement of the payment structure of his £25 million ($30 million) move from Celtic was eventually agreed on Wednesday night.

"It was the hardest decision in my whole life that I've had to make. I had to speak to my family and my close friends and my agent as well because it's a hard decision to leave a club that you love so much," said Tierney.

"I feel Arsenal is a massive club and it's a great opportunity for me as well. I'm delighted to be here."

Brazilian centre-back Luiz's £8 million move across London is expected to fill the void left by former captain Laurent Koscielny's acrimonious departure to Bordeaux earlier this week.

"David has huge experience and I look forward to working with him again. He is a well known player and adds to our defensive strength," said Arsenal boss Unai Emery.

Arsenal conceded 51 goals in the Premier League last season to miss out on Champions League football for a third consecutive season.

The double swoop would complete an impressive window for Arsenal despite missing out on the riches of the Champions League.

A club record £72 million was splashed on Nicolas Pepe from Lille to complete an exciting trio of attacking talent alongside Pierre-Emerick Aubameyang and Alexandre Lacazette.

Emery's midfield options were also boosted by the loan signing of Dani Ceballos from Real Madrid.