Lothar Matthaus said Bayern Munich should never have allowed Toni Kroos to join Real Madrid in 2014, but feels the transfer was a great move for the midfielder himself.
Kroos opted against renewing his contract at the Allianz Arena as he did not feel appreciated, prompting Bayern to cash in on the Germany international to prevent him from leaving on a free at the end of his deal.
The 27-year-old has since developed into a key figure at Madrid and Matthaus thinks Bayern should be regretting their decision to let Kroos leave.
"Bayern should have kept Kroos after he impressed at the 2014 World Cup," Matthaus wrote in his column for Sport Bild ahead of the Champions League tie between Bayern and Real.
"But he did not get the appreciation he wanted. He wanted to be on par with players such as Philipp Lahm and Mario Gotze when it came to his wages. And he did not feel valued enough as a player who came through the ranks of the club's youth academy. He was missing a certain recognition.
"There is always a lot of money in play when a star is brought in from another club. Kroos did not feel that same appreciation.
"Kroos did everything right with his move to Madrid. He has become a superstar there. A move abroad is a great step for a player's personality."