Both players were absent from the squad during Monday's preparations but were present for the opening session at Chelsea's Cobham Training Centre on Tuesday morning.
Gittens' return is particularly significant after the winger spent more than a month sidelined with a hamstring injury. His participation in training places him back in contention for selection for the European fixture.
James, meanwhile, was an unused substitute during Chelsea's tense FA Cup victory over Wrexham. The club captain is now expected to start against the French champions as Chelsea prepare for a crucial Champions League encounter.
Elsewhere in the squad, Cole Palmer, Moises Caicedo, and Enzo Fernandez were given the night off but are all anticipated to return to the group ahead of the trip to Paris.
Chelsea are still without Estevao, who remains sidelined with a thigh injury.
Another notable sight at Cobham was Levi Colwill, who has missed the entire season with a serious knee injury. While he remains unlikely to feature this campaign, his return to training has raised hopes of an earlier-than-expected comeback
Arsenal have received a timely injury boost ahead of their UEFA Champions League round-of-16 trip to face Bayer Leverkusen, with several key players returning to training on Tuesday.
Manchester City will host Liverpool in the standout tie of the FA Cup quarter-finals after the draw for the last eight was made on Monday.
Bayern Munich star Luis Diaz admits Atalanta won't be easy, emphasising the need for full commitment as the Bavarians travel to Bergamo for their Champions League Round of 16 clash.
Manchester City face uncertainty over Erling Haaland's availability as they prepare for their Champions League Round of 16 first-leg clash against Real Madrid on Wednesday at the Santiago Bernabeu Stadium.
