Ronald de Boer said it was impossible for brother Frank to succeed at Inter as the Dutchman slammed the lack of patience and outside influence in Milan.
Frank de Boer's tenure at Inter lasted just 85 days after he was sacked by the Serie A club in November.
There was a clear plan and tactic from Frank after he replaced Roberto Mancini on a three-year deal just a fortnight out from the start of the 2016-17 campaign but the former Ajax boss struggled to win over the players as he oversaw seven defeats in his opening 14 matches.
Ronald said the four-time Eredivisie-winning coach needed more time to implement his philosophy at San Siro.
"You're the man who's going to change the club, the philosophy. They wanted a different idea about football, to be more attractive," Ronald told Sport360.
"But you can't start here and go there without ups and downs. Of course if you're used to different styles, it takes a while. Look at [Pep] Guardiola at Man City. He's had unbelievable success but still it's not easy for him, and he's got even better players than Frank at Inter.
"Inter is a good team but if you want to have a philosophy you have to have time. If the results aren't there, they get impatient and there seemed to be too many captains on one ship.
"There was so much influence from outside and he had a group of 29 players which is way too much. You can imagine playing 11 v 11 in training and you still have to tell one player to warm up and he's still on EUR2/3million, and he can't even get in the second 11.
"He needed time to shape the system and implement his ideas so it was very hard for him, but I also think it was educational, he learned a lot. It wasn't to be but 85 days was terrible.
"Look at Alex Ferguson at Man United, he struggled for four years. If you believe he is the guy you have to give him a chance and they never gave him a chance. You don't have to feel sorry for him though. Life goes on and he's paid well, so next job."
Inter have since flourished, climbing up to sixth in Serie A and just two points adrift of the European places under Stefano Pioli.