Ethan Pinnock moved to the Reds’ Championship rivals Brentford this week, following out the exit door his former centre-back partner Liam Lindsay and goalkeeper Adam Davies, both of whom moved to Stoke City last week.
The trio each played more than 40 matches in the promotion campaign as the Reds kept a club record 21 clean sheets and conceded the fewest goals in the EFL.
Stendel told the Chronicle: “We lost the best two centre-backs in League One last season and also Adam Davies.
“Dani Pinillos cannot train at the moment (the Spanish left-back has had an operation on the eye he injured last season).
“It’s clear we made 21 clean sheets last season and had the best defence in the league which was a big point in our promotion. It is not easy to replace the quality and the experience we have lost.
“Especially with our style of play, it takes some time to get a player used to the behaviour of our defenders. But we do have some time so we will do it.
“We will train hard and give our best.”
Barnsley gave Pinnock his first taste of the EFL after signing him from Forest Green Rovers in the summer of 2017. The 26-year-old centre-back struggled for gametime in his first season, starting only nine Championship matches as the Reds were relegated.
But he started all 46 of Barnsley’s games as they gained promotion from League One last season, earning the fan-voted Player of the Year award and a place in the division’s Team of the Year.
This week the Reds recruited two players in his position, Finn Aapo Halme from bitter rivals Leeds United and Toby Sibbick from AFC Wimbledon.
The Reds had previously brought in goalkeepers Brad Collins and Sami Radlinger as well as winger Luke Thomas and centre-back Mads Andersen.
The three central defenders in Stendel’s first team squad are Sibbick, 20, and 21-year-old Scandinavians Halme and Andersen. They have played fewer than 100 matches between them and the only one with Championship experience is Halme who started one game at that level for Leeds. Stendel said: “That is Barnsley’s way. The club wants to develop players but the Championship is tough and we need a little bit more experience. We only have four or five payers who have played in the Championship. The quality of the teams is higher and I hope we sign some players who can help us.
“You can see Mads, Toby and Aapo have a lot of talent but I would like an older, experienced centre-back and I hope we can sign one. It’s not so easy to find a player with experience of the Championship and of the right age for the club, but I trust the owners.”
Reports of a bid from Championship rivals Millwall for top-scorer Kieffer Moore are understood to be untrue.
Stendel is a major admirer of Leeds United wideman Mallik Wilks, a 20-year-old who netted 15 goals on loan to League One Doncaster Rovers last season.
He is one of a number of wingers Barnsley are looking at.
The Reds have also been linked with Dynamo Dresden’s 22-year-old Senegalese striker Moussa Kone.