"They are the team to beat," England star Rooney told the official Champions League magazine.
"They are a fantastic team and people will remember what this Barcelona side have done for a long time to come, like the great Real Madrid and Manchester United teams.
"Their football is brilliant to watch and they win games playing that way, which is the main thing.
"Barcelona stand out for me. You can safely say if you beat Barcelona you have a good chance of winning the competition (Champions League)."
United and Barcelona are still involved in this season's Champions League, which resumes at the last 16 stage in February.
Barcelona will face Arsenal while United tackle French champions Marseille in the first knock-out round.