Philippe Montanier has said he believes his former protege Antoine Griezmann made the right move in joining La Liga champions Atletico Madrid.
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Striker Griezmann, 23, completed a 30 million euro switch from Real Sociedad on Thursday, signing a six-year deal with the Champions League runners-up.
The France international joined La Real in 2005 after failing to earn a youth academy place in his native country.
He developed into a major talent in San Sebastian, where he was coached by Montanier between 2011 and 2013.
Montanier, now coach of Rennes, told RMC he fully backed the forward's decision to join Diego Simeone's men.
"Even if he really liked it at Real Sociedad, and that he owes the club a great deal, to continue to grow he had to take a club on the next step up," he said.
"It won't be easy because it's a special club with enormous pressure, but he has always had his head on his shoulders. He knows what he wants.
"It's the logical move in his career trajectory. He has to keep the same mental freshness and the same enthusiasm."
Griezmann, unveiled in front of around 6,000 Atleti fans at the club's Vicente Calderon stadium, will wear the No. 7 shirt vacated by Diego Lopez.
"As soon as Atletico showed an interest, I didn't hesitate," L'Equipe reported him as saying. "They're a big club with a great project. We're talking about the Spanish champions and the Champions League runners-up.
"I have come here to learn. I needed to make a step up, and I have found the ideal place to do it. I have a lot of ambitions, starting with defending last season's league title."