Per Mertesacker
Per Mertesacker has played a crucial role in the back-line this season. Getty

Arsenal centre-back Per Mertesacker has praised Arsene Wenger's quick business during last summer's transfer window and suggested the fact the club's biggest stars remained in North London have been key to the Gunners' campaign.

Wenger had been heavily criticised in the past for waiting until the final days of the transfer window to complete signings, while also letting stars like Thierry Henry, Robin Van Persie, Cesc Fabregas and Samir Nasri leave the club.

But the French boss changed his transfer tactics in the summer of 2014 by breaking the bank to make the signings of Mathieu Debuchy, David Ospina, Calum Chambers and £32m Alexis Sanchez in July – with only Danny Welbeck joining late in the window.

Wenger sold out-of-favour Thomas Vermaelen to Barcelona but managed to keep his main stars at North London, including coveted midfielders Santi Cazorla and Mesut Ozil.

Mertesacker believes Wenger's transfer decisions proved crucial in a campaign which saw the Gunners finish third in the Premier League and retain the FA Cup.

"It was really important to get some early signings so everyone was on board for pre-season," Mertesacker told Arsenal Player.

"We were all excited about the new boys and how quickly they all settled. Every one of them gave a huge contribution to our squad and we didn't lose someone who was really a main part of last season's squad so it was a really good start."

The Gunners, meanwhile, are yet to make any signings this summer while Liverpool have already confirmed the arrivals of James Milner and Danny Ings and Manchester United have signed Memphis Depay.