The Brazilian midfielder has not featured since the draw with Aston Villa at Anfield in January due to a knee problem, while the Frenchman has been sidelined since suffering a torn tendon in his leg against Chelsea in December.
The duo played for the Reds' Under-21s side against West Ham last Friday and manager Brendan Rodgers is content that they are both ready to play their part for the rest of the season as his side challenge for the Premier League title.
He told the press on Friday of the state of his squad: "We're fine. We've had Lucas Leiva and young Sakho back in.
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"It shows you the commitment of this squad. They had an opportunity to have a break, they'd been working very, very hard with the medical team, but they decided to stay and last Friday they travelled down themselves in a car to London to play in an Under-21s game.
"Both came through that fine and they've trained very well this week. They come into the squad and we've only got Jose Enrique missing.
"Make no mistake, [Lucas and Sakho] are very valuable players for us in our squad and, if they're called upon to play or come off the bench between now and the end of the season, of course we will use them. Lucas and Mamadou have got great commitment to what we're doing and we'll welcome them back into the squad."
United have endured a disappointing first season under David Moyes but Rodgers warns that he will not be taking the Red Devils lightly.
"They're the champions and they've got players who are serial winners there. We're only concentrating on ourselves.
"They've got top players but I don't know the dressing-room well enough to understand where they are at."