Manchester United striker Wayne Rooney has admitted that Liverpool have been "brilliant" this season.
The champions have been forced to watch on as their fiercest rivals have mounted a Premier League title challenge, while United have struggled to adjust to David Moyes's reign.
The England international admitted that it has been "difficult" to see, but he also praised the Reds for their form.
Speaking to GiveMeSport.com, Rooney said: "Liverpool have been brilliant this season and it's probably their attacking qualities that has impressed me most.
"Luis Suarez and Daniel Sturridge are the Premier League's top scorers and have formed a great partnership, but they also have a lot of other players in good form like Raheem Sterling, Jordan Henderson and Steven Gerrard.
"They have been dangerous on the counter attack this season so that's certainly one thing we need to be prepared for and we will need to be tight at the back. There's no doubt that this is one of the biggest rivalries in world football. They are two massive clubs who have competed against each other for years and both have been very successful."
Brendan Rodgers's side travel to Old Trafford on Sunday.
