Bale hobbled off just 38 minutes into Madrid's 3-2 El Clasico defeat to Barcelona on Sunday on his return having also missed Madrid's previous two matches with an ankle injury.

"After the tests carried out today to our player Gareth Bale... he has been diagnosed with a grade two injury in the calf of his left leg," Madrid said in a statement on Tuesday.

The club didn't put a timeframe on Bale's return, but Spanish media, including sports daily AS, widely reported he will be sidelined for a month.

That would rule the Welshman out of Madrid's two Champions League semi-finals against Atletico Madrid and Real's remaining six La Liga games.

However, should Real see off Atletico in his absence, Bale could be fit in time for a homecoming in the Champions League final in Cardiff on June 3.

Bale has made just 26 appearances in all competitions for the European champions this season, scoring nine goals.

He missed three months of action between November and February due to ankle ligament damage.