Wenger signed a two-year contract to remain as Arsenal boss on Wednesday as the club's hierarchy demanded a serious push for the Premier League title.
The Gunners manager won a record seventh FA Cup last weekend, but failed to qualify for the Champions League for the first time since he arrived in 1996 after finishing fifth in the table.
And Pires has urged Wenger to splash the cash this summer if he's to win the Premier League for the first time since the famous 2003/04 Invicibles season.
Pires spent six successful years under Wenger between 2000 and 2006, winning seven honours during his time at the north London club.
Arsene Wenger signed a new two-year deal after winning FA Cup
Now it's very important to buy players and build a team to win the Premier League
Arsenal legend Robert Pires
Talking to Sky Sports, Pires said on his former club and manager: "I love Arsenal and I love Arsene Wenger so I think it's great news for him.
"I think the decision is not easy because they had some trouble during the season with some fans, so now we need to build a new team for next season.
"Some fans are split but the message is to be passionate for next season because the first objective will be to win the Premier League.
Robert Pires urges Arsene Wenger to splash the cash this summer Who Arsene Wenger could axe and who he could sign in Arsenal revamp Wed, May 31, 2017
Arsene Wenger has signed a new two-year deal with Arsenal but who could he sign and who could he axe in a mass overhaul at the Emirates?
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"I think Arsenal will be stronger for next season. Now it's very important to buy players and build a team to win the Premier League."
Wenger remains confident in his Arsenal players and believes they are now in a strong position to challenge next year.
"We're committed to mounting a sustained league challenge and that will be our focus this summer and next season," he said after putting pen to paper on his extension.
"They are of course unlimited, our ambitions. We live in a very competitive world where you need the support of the owner as well."