Chiesa recently joined from Italian giants Juventus and took part in the young Reds' Thursday session which Lewtas said is a big learning opportunity for the up and coming talents.
"We've been coming round here for a while and the first-team players, their level of professionalism is unbelievable, it really is.
"Obviously you can see from the quality of his career so far, this is why he's at one of the best clubs in the world. His professionalism and his quality was really good.
"It obviously just gives our boys a little bit of a chance to play against someone of that quality (and) it's a really good learning opportunity for them.
"I think any time when we come round to the first-team side, which we do a lot, is always really good. It's a change of scenery but also more importantly gets us around first-team players and first-team staff, which is important for the boys."
Young star Rio Ngumoha made headlines for a few clips of his ability this week as well. Lewtas praised the 16-year-old who has just arrived from Chelsea.
"It's a nice introduction for Rio," Lewtas continued. "It's a chance for him to get to know the U21 players and an opportunity to train as well with the first-team staff.
"Getting to know people as soon as you come is really useful because it helps you settle, it makes you more familiar and it gives you that grounding.
"Obviously with Federico, we've done this a number of times now (where) we'll bring boys round, and it gives him a chance to build his fitness and get him ready for the season as well."