Instead, his collision with Benfica goalkeeper Artur late in Wednesday's Champions League match may only rule the Barcelona forward out for one match.
"I sincerely thought it was the last ball I would be touching for a long time because of the pain," Messi said Thursday. "I tried to go ahead and shoot but I didn't have the strength."
Messi collided with Artur in the 85th minute of the 0-0 draw while trying to score a goal that would have put him even with Gerd Mueller with the most goals scored in a calendar year. Barcelona fans at the Camp Nou then watched silently as he was taken off on a stretcher.
The 25-year-old Argentina international is trying to break Mueller's 40-year-old scoring record. He has scored 84 goals in 2012 and has four games to catch Mueller, who scored 85 for Bayern Munich and West Germany in 1972.
Messi said he could miss Sunday's league match at Real Betis, but had originally thought his career was in jeopardy.
"I feel much better than yesterday. I don't know if I will be there on Sunday," he said. "It depends on how (my left knee) progresses.
"I didn't think anything when it happened. I just believed from the pain that I would be sidelined for a long time," Messi said. "At that moment I thought the worst. Later, when the doctor examined me in the changing room and ruled out a serious injury, it was a relief."
Barcelona coach Tito Vilanova sent on Messi with about 30 minutes to play even though Barcelona entered the game with first place in their group guaranteed. In his first season since taking over from Pep Guardiola, Vilanova has led Barcelona to a record start in the Spanish league with 13 wins and a draw.
Messi said he had no regrets about playing the game.
"What happened to me yesterday could have happened to me in practice or any game," Messi said. "In the last five years, since Guardiola arrived, it has always been like this. When we weren't playing for anything I would still play a few minutes. Under Tito it has been the same."
Messi was prone to injury in his early years with Barcelona's first team after coming up through its youth academy. But Guardiola's return to coach the team in the 2008-09 season coincided not only with a leap in Messi's development as a player, but also with him becoming much more durable.
The last time Messi missed a match due to injury was in September 2010.
Messi is one of three finalists for the FIFA world player of the year award to be announced on Jan. 7. He is trying to become the first player to win the award four times.