Wales international Bale has been plagued by niggling muscle injuries since moving to Spain in 2013 but said he was ready again to put his "strength and speed" at the team's disposal after shaking off a calf problem.
Bale sustained the injury in the La Liga win at home to Levante on Oct. 17 and missed four matches before returning for the 3-2 defeat at Sevilla in Real's last outing.
"I haven't had a chance to play much this season," he told Real's website (www.realmadrid.com) on Thursday.
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"Nowhere near as much as I would have liked anyway, but I'm feeling strong and fit for this game," added the 26-year-old.
"I'm ready for battle. I want to keep trying to give my best, to work hard and to help the team win."
Real surrendered top spot to Barca when they were beaten at Sevilla and another defeat on Saturday will see them drop six points behind their arch rivals after 12 games.
Atletico Madrid, the 2014 champions, are a point behind Real in third ahead of their match at Real Betis on Sunday.
Bale noted that Real, who replaced coach Carlo Ancelotti with Rafa Benitez at the end of last season, have lost only one match this term but said there was "some room for improvement".
"We could still be better, play better, and I'm hoping that, as the season goes on, our form continues to improve and that leads us to winning La Liga," Bale said.
"I'm certain you'll see an attacking game from both teams and it makes sense that the team that scores a lot of goals will win.
"I'm hoping they don't score many. It will be an even contest, it's always tough against them, but fingers crossed we're able to get more goals than them."
(Writing by Iain Rogers in Madrid, editing by Toby Davis)
