The Dutchman believes his former Barca team-mate will miss the Argentine forward but has stressed the Bavarians still have plenty of quality
Attackers such as Arjen Robben and Franck Ribery have played a key role at the Bundesliga champions in recent seasons, yet Koeman feels they are not at the same level as Messi and he is curious to find out how Guardiola will fare without the Argentine.
"At Barcelona, Pep had Lionel Messi in his team, who could single-handedly decide matches," Koeman was quoted as saying by De Telegraaf.
"In my opinion, Bayern Munich do not have a similar player."
However, Koeman still thinks the Bavarians have plenty of quality, even without a player like Messi.
"He has inherited a fantastic team and then Bayern are also able to sign an amazing player like Mario Gotze. The players at his availability should not be the problem."
Koeman played alongside Guardiola at Barcelona from 1990 until 1995 and his former team-mate's success as a coach does not come as a surprise for the Dutchman.
"It's only logical that he became a coach. I didn't see it right away, because he was still in the early stages of his career when we played together. But he had fantastic qualities as a footballer. He had superb vision, was a real teamplayer and was always thinking about tactics."