Victor Orta has confirmed to the YEP in an exclusive interview that Norwich City man Cantwell and Derby County youngster Sibley have been monitored.
But as we reported last week, a new arrival before Friday's domestic deadline is still understood to be unlikely.
Norwich midfielder Cantwell has been linked to a move to Elland Road for weeks, while Derby County youngster Sibley has only recently emerged publicly as a player of interest.
Leeds wanted to add a midfielder to their squad before the international transfer deadline passed, but a move for Bayern Munich's highly rated Michael Cuisance fell through.
Although Leeds and Bayern reached agreement over a deal in the region of £20m for the 21-year-old, concerns were raised at the Premier League club over his medical and he flew back to Germany, before joining Marseille on loan. Leeds moved on and signed winger Raphinha from Rennes on deadline day.
It was disappointing for Orta but the director of football was philosophical.
READ: Part two of our exclusive interview as Orta talks Rodrigo De Paul and Ryan Kent"It's a part of the situation," he told the YEP.
"We analyse all and at the end if things happen, no agreement. These kinds of things happen. It's part of the market. It's disappointing but it's part of the process."
When asked why no midfielder has been forthcoming, given the club were willing to part with so much money to bring Cuisance to Elland Road, Orta simply pointed to the standards Leeds have for any player joining Marcelo Bielsa's squad to rival or cover for Mateusz Klich in midfield.
In the international market, the right player was not available.
"When we analysed the market we detected that with the requirements we have for this position, if a player is not realistic over all the requirements, bringing in a player for the sake of bringing in a player is not clever," he said.
"It can be worse. We prefer to bring in a good player."
The domestic window allows Leeds to sign players from EFL clubs. It doesn't shut until 5pm on Friday, giving Orta more time to address the midfield needs.
But, like the January window, this one has its limits for the Spaniard.
"We are analysing but obviously the market is greatly reduced now," he said.
"Even for us it's difficult to evaluate clearly one point of view. The availability is reduced from the other market."
As for Cantwell and Sibley, Orta made no secret of the fact that they have been considered by his recruitment team. The YEP understands that Leeds' consideration of the latter has gone as far as making enquiries for the 19-year-old attacking midfielder, who scored a hat-trick against Leeds Under 23s last season and featured in the Championship game at Pride Park, but there are currently no plans in place to make a move before Friday's deadline.
"We analyse all the players," he said.
"We know them really well, their clubs were our rivals, we analysed [Cantwell] in the Premier League. But it's like a lot of players we've analysed.
"It's difficult. They are players we analysed, we have information and then we need to think about the possibility."
READ: Part three, Orta explains Leeds United's new loan policyAs ever, for Orta and his team, information remains king and will allow them to make swift decisions if circumstances change - as they often do - in this transfer window or the next one, which opens in January. He says the plan for the winter window is simply to be ready to use their information to react to the needs of Bielsa or any shifts in availability when it comes to targets.
"We are always focused on information, managing it, analysing players, their availability, staying updated," he said.
"That could be useful for the winter market. We need to put in practice the usefulness of the knowledge."