Bayern Munich were 'naive' against Kylian Mbappe and Paris Saint-Germain and must wise up for the second leg, Bixente Lizarazu has said.
Mbappe scored twice as PSG claimed a 3-2 first-leg win over the holders in their Champions League quarter-final encounter in Germany last week.
PSG had 36 per cent of the possession and just six shots to Bayern's 31 but made the most of some clinical counter-attacking play as Mbappe and Neymar exploited the hosts' high defensive line.
By contrast, Bayern – who had an expected goals figure of 3.8 for the match, compared with PSG's 1.3 – could not make the most of their chances in the absence of the injured Robert Lewandowski.
Lizarazu, a Champions League winner in 2001 during a glittering career with the Bundesliga giants, fears Hansi Flick's side could suffer a similar fate against Mbappe in the second leg if they do not make changes to their defensive approach.
"If Bayern play so naively by leaving such a large space behind their defence, Mbappe will express himself in the same way," he told Telefoot.
"Mbappe is really strong in there. He's the best forward in the world on the break or in quick attacks. Can Bayern correct that, or not?"
The future of Mbappe – who has 33 goals and 10 assists in 39 appearances this season – remains the subject of intense speculation, with Real Madrid said to be keen to sign him in the next transfer window.
The France star has just a year left on his contract and, if he does not commit to a new deal, Lizarazu has encouraged PSG boss Mauricio Pochettino to seek a reunion with Tottenham's Harry Kane.
"I would do anything to keep Mbappe. If he has to leave, Kane would be a good reinforcement for PSG," Lizarazu said.
"You need a centre-forward who is both a goalscorer and who can play, such as Lewandowski can do at Bayern."