The Championship strengthened their defensive options before Friday's loan deadline, bringing in Michael Hector on a season long-loan from Chelsea.
Although Hector has not played a first-team match for the Blues since since joining for Â£4m in 2015 from Reading, he possesses plenty of experience at this level. He spent last season on loan at Hull City, appearing 38 times in the Tigers successful bid to avoid the drop.
Luhukay told The Star: "We cannot forget that we gave eight players away (over the summer).
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"We gave Glenn [Loovens] away and Frederico [Venancio], who play in central defence, and we gave Jack Hunt away as a right sided defender.
"At this moment, we have no problem. But for example when Tom [Lees] had an injury in the past, we had no depth in that position.Â
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"We have Freddie Nielsen, who is a young player from the academy. He played against Wolves but it is a position where we didn't have a lot of choice."
Both Hector and Onomah, who were ineligible for Saturday's victory over Reading, are currently away on international duty with Jamaica and England's Under-21s respectively.
'It is a positive situation for our club that we have signed these two players," he said. "We hope these players give us extra quality.
"It is very important you have competition in positions. It brings a high level in the team and spirit. You know you can't rest as a colleague could take the position."
On the possibility of turning their loans into permanent deals, Luhukay said: "First of all, we only speak about loan. Let's see what the future brings us."