Napoli s Nigerian forward Victor Osimhen. AFP
The 24-year-old had been linked with several clubs, with reports suggesting that Premier League giants Manchester United are preparing a £130 million bid to hire the player, who was also chased by Bayern Munich and Chelsea.
"When it comes to such a fee, we have to ask the question: does the player give you a guarantee for this money?" Oliver Kahn told German magazine Bild on Wednesday.
"That would definitely be a big risk."
Napoli chief Aurelio De Laurentiis has stressed that the Nigeria international will remain at the Serie A club, and the player himself has played down departure rumors. However, United believe their lucrative deal could convince their Italian counterpart.
Osimhen was instrumental in Napoli's triumphant campaign this season, which saw them win their first Scudetto in 33 years earlier this month after scoring 23 goals.
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