The 37-year-old Poland captain sustained the injury during his national team’s 2-0 win over Lithuania in a World Cup qualifier in Kaunas on Sunday.
"Robert Lewandowski has suffered a hamstring injury in his left thigh," the club said in a statement.
"He will be sidelined, and his recovery time will depend on how the injury progresses," it added.
Lewandowski said he began feeling pain in the first half after a challenge by a Lithuania player and asked for his thigh to be wrapped at halftime. He finished the match despite discomfort.
According to Polish media, the forward did not report the injury immediately after the game and was not sent for tests before returning to Spain.
Polish state news agency PAP reported that Lewandowski is expected to be out for about three weeks, missing upcoming La Liga matches against Girona and Real Madrid, as well as a Champions League fixture against Olympiacos on October 21.
In the worst-case scenario, he may also sit out Poland’s World Cup qualifiers against the Netherlands and Malta in mid-November.
Lewandowski has scored four goals for Barcelona in nine La Liga appearances this season, along with two for Poland, including one against Lithuania last weekend.
(gs)
Source: PAP, fcbarcelona.com, polskieradio24.pl, przegladsportowy.onet.pl