Barcelona coach Pep Guardiola is wary of the strength of Manchester United's squad ahead of Saturday's Champions League final at Wembley.
United beat Schalke 6-1 on aggregate to reach the final, winning the second leg 4-1 after making nine changes to the side that had triumphed 2-0 in Germany.
Guardiola, whose side beat Real Madrid 3-1 in the last four, said: "United can field five teams that are competitive.
"I watched them play Schalke, they made nine changes and still won easily."
He added: "I can't make nine changes to my team because we have a small squad, but they have so much quality - [Dimitar] Berbatov, Chicharito [Javier Hernandez], [Wayne] Rooney, [Paul] Scholes, [Ryan] Giggs - they have so many players to choose from."
The two sides are meeting for the first time since Barca beat United 2-0 to win the 2009 title in Rome.
Diminutive Argentine forward Lionel Messi scored the second goal in that victory as Barca wrapped up a Treble of Primera Division, Copa del Rey and Champions League titles in Guardiola's first season in charge.
However, Messi stressed that the result in the Stadico Olimpico will have no bearing on this weekend's match.
"I have good memories of the final in Rome, but that's in the past," he said.
"All finals are different and this will be a totally different game to that one - United have changed [some of] their players and it will be different.
"They are not weak; they have very good players and a lot of quality up front - and they are used to winning.
"I don't know how they will play but it will be a special game and we will look for their defects."
Fellow Barca player Daniel Alves also believes the current United team is a tougher unit as they are much more unpredictable without Cristiano Ronaldo, who they sold to Real Madrid for £80m during the summer of 2009.
The Brazilian, who was suspended for the 2009 final, said: "You can see now that they have built a much more balanced side, stronger than a couple of years ago.
"They are dangerous across the board and packed with great players."
Barca and United are both hoping to win a fourth European Cup, which would put them level with Dutch side Ajax and Bayern Munich of Germany.
Only Liverpool, with five victories, Italian side AC Milan (seven) and Spaniards Real Madrid (nine) have won more.