Jose Mourinho believes Lionel Messi alone is capable of changing the balance of power for any club in the Champions League.
"I am saying that a team with that boy is a different team, is a different story," Mourinho said on Friday.
"Every time I played against Messi, I spent hours studying and trying to stop him," Mourinho said. "Many times, we were successful, other times we were not successful.
"With Inter [in the 2010 Champions League semifinal], we stopped him in both matches -- Inter-Barcelona and Barcelona-Inter. The best way to [usually approach] is man-to-man because that is better than involving everyone," he continued.
"When you go man-to-man you go with similar power, although man-to-man with him is an impossible job. Like I say, sometimes I was successful, sometimes I was not successful."
"Every time I was thinking about how best [to] collectively -- I am not saying stop him -- give him a difficult match. I think this is the correct word. It is not about stopping him but giving him a difficult match. That is the best you do against him."
Mourinho also argued Messi makes the very idea of systems almost irrelevant.
Luis Enrique's entire gameplan with Barcelona at this point appears to boil down to the imperious form of Messi.
"People think in the wrong way," Mourinho said. "One thing is a team. Another thing is a team with Messi. It is a different story. He played a Champions League final with [Frank] Rijkaard. He played a Champions League with Guardiola. He [if it goes as expected] is playing a Champions League final with Luis Enrique.
"So, when people analyse teams, you have to remember that this boy makes everything different. He makes everything different.
"I think this guy makes the gap by himself. You have doubts that [Manchester] City with Messi can win the Champions League? Or Arsenal with Messi can win the Champions League? Or Chelsea with Messi can win the Champions League? Or Man United with Messi can win the Champions League? Don't you think? I think.
"I am saying that a team with that boy is a different team, is a different story."