The Reds' promotion push suffered a major blow last week when Brad Potts opted to leave the club and jump up to the Championship withÂ Preston.
The midfielder played an integral role in Daniel Stendel's side's rise to fifth in League One, scoring seven goals, but Winkler said the deal was too good to turn down.
OtherÂ BarnsleyÂ players have also enhanced their reputations under Stendel this term, leading to transfer speculation, and Winkler could not give any assurances.
'We were really disappointed that he (Potts) left us,' the German said.
'He was a good player and a very nice person. But that is how it is in the transfer window, players go and come. We have to go on and look forward.
'We didn't want him to go, but sometimes it is necessary.
'In this case, we didn't expect them to put up such a good offer toÂ Barnsley, the amount we cannot believe that. For League One it is a lot of money.
'But now we go on, we have some good attacking players in our squad. I hope no more players go, but I cannot make any guarantees.
'But I can guarantee everyone at the club wants to give us a strong squad to go for promotion. That is professional football, you never know.'
Winkler takes other clubs' interest inÂ BarnsleyÂ players as a compliment.Â Â Â
He said: 'That is how it works, thin lines, doing a good job and good performances, enjoying it a lot.Â Â But, on the other hand, all the other clubs' recruitment guys look at us.
'If you look at the list every Saturday at our home games, they come from everywhere in the country, andÂ Europe,Â to watch our squad.
'There is a lot of interest in our players. We take it as a compliment. It is not only the players doing well, it is also because they implement our style of football.
'That is also a reason why the players are doing well and why we are one of the top teams in the league.'
The Tykes are looking to extend their unbeaten league run to six matches in the Yorkshire derby at Oakwell on Saturday.
They host aÂ BradfordÂ side that, despite languishing in the relegation zone, have won four of their last five matches.Â Â
And Winkler said: 'They have a winning run, they are doing really well and have lots of confidence. We expect a tough match.'