Barcelona's Lionel Messi kicks the ball to score his second goal against AC Milan during their Champions League soccer match at Nou Camp stadium in Barcelona, Nov 6, 2013. [Photo/Agencies]

Barcelona star Lionel Messi will be sidelined for 6-8 weeks due to a muscle tear in his left hamstring, the Spanish club said on Monday, his third leg injury this season.

The 26-year-old Argentina international limped off after just 20 minutes of Barcelona's 4-1 win over Real Betis on Sunday and was replaced by Andres Iniesta.

It was the third time this season he has been forced off with a muscular problem following hamstring and thigh injuries to his right leg.

"The club's medical services confirmed after tests this Monday morning that Leo Messi has a torn hamstring muscle in his left thigh and is expected to miss the next six to eight weeks," Barcelona said.

"The first phase of Messi's recovery will be covered in Barcelona and he will then travel to Buenos Aires," it said.

That means Barcelona will be without Messi for up to eight matches, including its lasts two Champions League group games against Ajax and Celtic.

After Sunday's match, Barcelona boss Gerardo Martino said Messi's injury troubles were not related and the absence of the four-time World Player of the Year could never be used as en excuse for the team to not perform.

"We have the best player in the world, but we also have four or five of the next six or seven best players in the world. Therefore, as a coach, the absence of Messi should never be used as an excuse for not winning.

"The injury to Messi doesn't have anything to do with the previous ones because it is the other leg.

"We also need to speak with Leo, it is the third episode he has had in a short time so it is obviously playing on his mind."

Messi suffered a bruised thigh during the first leg of the Spanish Super Cup against Atletico Madrid which kept him out for a week.

He then suffered a small muscle tear in his right thigh during a La Liga match against Almeria on Sept 28 which sidelined him for three weeks.

Last week Messi said on Chinese networking site Weibo he was still not fully fit.

"Physically I am still not at 100 percent but I am confident that as I play more matches I will recover my rhythm," he said.

Teammate Cesc Fabregas said he understood Messi's frustration, but that it was possibly best for his teammate to sit out a couple of weeks.

"Messi needs to be explosive to stand out and he needs to stop for as long as it requires to be OK," the midfielder said.

Barcelona has 37 points from 13 games, three ahead of second-placed Atletico Madrid.