The Uruguay striker became the first Reds player to bag back-to-back league hat-tricks on the same away ground in Saturday's 5-2 victory at Norwich City.
"It's a privilege to be able to play alongside Luis," Allen said. "I'm just grateful he's on my team. When you're out there playing alongside him you just have to be in awe of a performance like that.
"The goals, some of the things he did, not many people in world football can do.
"He's got everything you need to be a top-class striker and I'm excited about the season he's going to have for this team."