The Chile international, who was also targeted by Manchester City, completed his move to Barcelona from Italian side Udinese late last week and will be presented to the press today.
"Alexis Sanchez is a superb signing for Barcelona," Europa Press quotes Messi as saying. "He has a lot of qualities and I think that he fits in very well at the club. I've seen him play a lot and have known him for quite a while. He is a fantastic player."
The 24-year old, who won both the La Liga and Champions League titles with Barcelona last season, added that the side are hungrier than ever ahead of the 2011/12 campaign.
"We have made history in the past couple of years," he continued. "Everything that has happened is simply fantastic. We are extremely motivated to keep going and have fun out there. We want to bring joy to our fans."
Barcelona will next face Brazilian side Internacional in a friendly on Tuesday.