Jens Lehmann has insisted that Aaron Ramsey will have to leave Arsenal in the future if he wants to become a top player, but that time is not now.
Instead, Ramsey must first prove he can be available for a full season, avoiding injury and staying consistent for the Gunners.
Ramsey has been the standout player for Arsenal this season, culminating in his winner in the FA Cup final against Hull City. That was his 16th goal of the season - a truly sensational stat for a midfielder who spent three months in the treatment room.
Lehmann says it is Ramsey's, 23, tendency to get injured that is holding him back from making a big move this summer. Once he proves he can last an entire season without injury, he should consider a move to a club like Bayern Munich or Barcelona.
The German told BBC Wales: "There are some really great clubs and only probably 100 top players.
"So when you want to be a top player you need to try your luck somewhere else and you want to find out if you can manage to be successful somewhere else as well.
"But so far I think it's a step too early because he himself has to make sure that he can be available for a whole season."
The former Germany international, who was part of the famous Invincibles team in 2004, says he has been surprised by Ramsey's excellent form.
"Ramsey was a surprisingly fantastic server of the club because when you've looked at the seasons before, he was good, but not that outstanding," said Lehmann.
"And all of a sudden he knew how to score; he found the goal quite often.
"Unfortunately - and that's what he has to work a lot on - he got injured again.
"And when you want to become a world class player, the first thing is that you're always available.
"But when you're not always available you can be as good as you want, but you will lose your rhythm and, slightly, your physique.
"And that's what Arsenal can't have with Aaron because Aaron was such a great character and talent that he has to be available all the time."
Luckily for Arsenal, they tied Ramsey down to a long-term contract earlier this season, bumping up his pay up to £100,000-a-week and tying him down until 2019.