Ronald de Boer insists Rangers will have to wait if they want to hire his brother Frank as their new boss.
Frank, who played at Ibrox alongside his twin in 2004, has been tipped to take over after Mark Warburton's exit.
But Ronald said a bad experience at Inter Milan means Frank will never again enter a job at what he considers the wrong time.
"He will never take a team at this time of year," he told BBC Radio Scotland's Sportsound.
Frank left Ajax for Inter in August 2016 but was sacked after just three months.
And he blamed a lack of pre-season preparation time for the problems that blighted his time in Italy.
"Frank won't go into that (whether there has been an approach from Rangers) but he told me, and I knew this already, that he's waiting probably until the end of April and then he will take his decision on what options are on the table," Ronald added.
"He wants to have a decent run-up. He had this lesson with Inter Milan when he had only two weeks to start the league, he couldn't really prepare the team. I think he learned from that so he wants to have a good pre-season and get to know the players very well.
"He will never take, for example, the Rangers job just now. That's not in question."
And Ronald insists his brother would asses whether Rangers could adapt to his playing style before making any decision.
"He has his philosophy," he added. "Do they stand close to his philosophy and how he wants to play? Is there a chance to buy players, all these kind of things.
"He has to observe the team itself, how strong it is and are the players able to fulfil his thoughts? Frank will play forward so he wants players who can play in small spaces, who can dribble and are willing to go forward. That's really important."
Warburton left Ibrox with Rangers sitting third in the Premiership table, having led them to promotion last season.
And Ronald has sympathy for the Englishman, insisting finances dictate that Scottish clubs must now show more patience with managers and players, much like in his native Netherlands.
"Of course (I have sympathy for Warburton)," he said. "You have to be patient, take your time and of course some players will do great in the Championship and then when you come to the Premiership it's different.
"Sometimes you have to see it happen and then you can judge certain players, because the pressure is suddenly way higher.
"The money is not there anymore, it's in La Liga or the Premier League, in the German league, the Italian - even the French league is more exciting than the Dutch and the Scottish. It's very difficult so we have to accept we have to build with young talent and have to be patient."