The head coach appointed the 24-year-old as skipper on the eve of the new season, picking the South African-born player to replace Adam Rossington who had been at the helm since the middle of the 2019 season.
But Vasconcelos's tenure as captain has lasted just eight matches and four months, with the player deciding he now wants to concentrate solely on his own batting after a difficult season so far by his own high standards.
Sadler admits Vasconcelos's decision was not expected, but he fully understands the player's reasons.
"Ricardo was offered the job at the back end of March or whenever it was, and the attributes he had suggested he would be the right man for the job," said Sadler.
"I still think those attributes are there and in place, but in his words it has taken up a bit more time and focus and taken more energy away from his own game than he anticipated.
"He came in full of optimism and with full commitment and he gave it his best shot, but on reflection he feels it is time for somebody else to take over.
"We fully respect his decision, and look forward to seeing him back at his best.
"Captaincy is still something he may want to look at down the line, but certainly in the short term he wants to focus purely on his batting and his game, and to contribute to this team with runs."
As an opening batter, Vasconcelos has struggled for form so far this season, although he did hammer a superb 156 against Warwickshire at Edgbaston in May.
But take that innings away, Vasconcelos has only scored 189 runs in 12 innings at an average of just 15.75.
Sadler believes opening batters can make good captains, and that the job was perhaps just too much for Vasconcelos to take on at this stage of his career.
"A lot of opening batters have been successful captains, there is no doubt it can work," said the head coach..
"But there is no set formula, there is no hard and fast rule about how things need to be done.
"Ultimately, Vasco gave it his best shot, and on reflection he feels it has affected his game more than he thought it would.
"He is now ready to step down and let somebody else crack on."