Lampard believes the blues have missed RLC's goals after the England man has returned from injury to begin light training sessions.
"I think you will miss Ruben; I don’t care who you are. You’ll miss his abilities. His natural physique, his ability to move the ball well and score the goals like he did last season, that has to be a big part of his game as well," Lampard told reporters.
"Of course, we’ve missed a player of that level and it is nice and put a smile on everyone’s face on Friday because he is popular with his team-mates too. A smile on everyone’s face to see him back.
"It was the first day with us fully on Friday and it was a light session so that suited him. He has a fair way to go still, and I'm not pessimistic there. He just needs a full week training with us first, a tough week.
"Then he will need some U23 games, and again I think the break comes at a nice time for him to work and we’ll gauge it the other side of that break and see where he is. It might be too early [to face Leicester in the U23's on Friday].
"The week’s training is the important thing because he hasn’t had that at first-team level. Then we will consider the games after that."
Chelsea beat Hull City 2-1 away at the KCOM Stadium but the next face Leicester City in the Premier League who currently sit above them in the table in third place.