The midfielder, 32, recently signed a short-term deal with the Cottagers until the end of the season.
Gale now hopes that Diarra, who spent just over a year at Craven Cottage before being released last summer, can help the team pull away from the bottom of the table in the final few weeks of the campaign.
"He's worked hard to get back to fitness and it gives us another body which we'll need in the run-in," Gale told the club's official website.
"Hopefully he can play a part having been out for so long. Fair play to him because some players might have called it a day but he refused to give up and the hard work has paid off."
Fulham continue their Premier League campaign this Saturday at Aston Villa.