Modric came on for the final 20 minutes of Wednesday's 0-0 Champions League draw at Paris St Germain, his first appearance since he damaged a thigh muscle playing for Croatia in this month's Euro 2016 qualifier against Bulgaria.
Real have missed the control he provides in the middle and have also been hampered in recent weeks by the absence through injury of forward Gareth Bale, striker Benzema, playmaker James Rodriguez and captain and centre back Ramos.
Benitez said Friday's training session would give him a better idea of who was fit to play at Celta's Balaidos stadium, with the two unbeaten sides level on 18 points at the top with champions Barcelona after eight matches.
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"We have training now so we will see how the players are progressing," Benitez told a news conference on Friday.
"These are decisions that depend on the level of risk we want to run ... and on what the team needs," he added.
"Modric is fine, he trained and played so in that sense we are more optimistic."
Bale, Benzema and Rodriguez are not in the squad for the trip to Galicia, while Ramos, who is recovering from a dislocated shoulder, is travelling, Real said in a statement on their website (www.realmadrid.com) later on Friday.
Modest Celta have outperformed this season and the Galician club inflicted the biggest La Liga defeat on Barca, excluding games against Real, in more than a decade when they thumped them 4-1 at the Balaidos last month.
"We know it’s going to be a very tough match because as you say they have not lost a game yet and they play with a lot of intensity," Benitez said.
"As is always the case with all the teams in the world when they are playing Real Madrid, they will try to give their all and will have the extra motivation of being at the top of the standings.
"Of course having to play again after only two and a half days is a small handicap but we have sufficient quality to cope and to win the match so we can take the three points back to Madrid."
(Writing by Iain Rogers, editing by Ed Osmond)
