The Argentine World Player of the Year collapsed to the turf after colliding with Benfica goalkeeper Artur late in the Group G clash at the Nou Camp, which ended 0-0, and was taken off on a stretcher in obvious pain.
A scan ruled out anything more serious than bruising and Messi worked out in the gym on Thursday.
"When I felt the blow I thought the worst because of the pain, that I might be out for many months," said the 25-year-old who came on as a substitute for the final half an hour with Barca already through to the last 16 as group winners.
"After the tests, and having ruled out a serious injury, I was much more relaxed," he said. "I am feeling good, fortunately it was only a blow and I am much better."
After his collision with Artur, Messi still managed to fire a shot away which the Benfica keeper saved on the line. "I thought it might be the last ball I kicked for a long time and I wanted to take the shot," Messi said.
"I don't know if I'll be available for Sunday, it depends on how things go. You won't notice (if I am out) because there are plenty of other players."
Messi last missed a game through injury in September 2010 when he was out for two matches with a damaged ankle following a crunching tackle from Atletico Madrid defender Tomas Ujfalusi.
Barca coach Tito Vilanova was questioned about the wisdom of bringing Messi off the bench in a largely meaningless match but the player noted that injuries can happen at any time.
"I still think the same, that it could have happened in training or in any other match," Messi said. "Whenever you go on to the pitch there is a risk."
He said he was not obsessed with breaking the record for the most goals in a calendar year of 85 set by former Germany and Bayern Munich striker Gerd Mueller in 1972.
Messi has 84 for club and country in 2012, including 21 goals in 14 La Liga matches this season and another five in his six Champions League outings.
"Obviously it would be nice because it (the record) was set many years ago and I am close, but it doesn't worry me," he said.
Barca have three La Liga matches and the first leg of their King's Cup last 16 tie against Cordoba left to play in 2012.
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