The Blues partook in a full session of strength and conditioning training at Cobham headquarters on Wednesday afternoon, complete with giant Swiss balls, resistance harnesses and medicine balls.
Chelsea have been criticised in the past for not giving Lukaku a chance and the club have faced similar ridicule this season following the stunning campaigns of former players Mohamed Salah and Kevin De Bruyne.
Meanwhile, Willian has made over 200 appearances for Chelsea since joining the West London club back in 2013. They've gone on and developed elsewhere, and he's gone on to be a top player.
Jose Mourinho's side received a massive boosted by the return of Lukaku, who missed their last three League games of the season with an ankle injury.
Chelsea midfielder Cesc Fabregas has called on his team-mates to "feel the fire inside" as they prepare to take on Manchester United in the FA Cup final on Saturday.
"The Cup Final is the Cup Final, it is the pinnacle of the season, and I just hope it lives up to expectations". "We've been involved in a lot of Community Shield games and that's one we relish and we like facing tough opposition as well".
"The one under Van Gaal, I wasn't playing, so that was OK - not OK, but reasonable", the 26-year-old said. Our fans deserve more than today'. "If a European team, like, very European, could have a Brazilian in their squad, it would bring a "Brazilian thing" to the game and I think that's very important".
"Every single one of us has got to stay focused, do what the manager asks of us to do on the pitch and try to win", he said. The match is a last chance for silverware this season for both clubs and Cahill believes that the Portuguese head coach will have put in place a detailed game plan.
A number of Chelsea's players will face their old boss on Saturday, with Mourinho leading out United once again.