Bueno, who is 21, broke through into the first team picture during the last campaign.
However, injuries and Rayan Ait-Nouri starring at left-wing-back means he has not gotten much game time.
It's an unfortunate season for him so far," O'Neil said of Bueno to reporters.
When I first arrived he was doing really well. Him and Rayan were pushing really hard for the same spot and it was fairly fluid between who got the nod.
Then he suffered the injury at Ipswich and missed a few games. Rayan did well and when he came back he'd have probably played in one of the cup games but had a sore calf. Sometimes things like that go against you enough that someone comes in and does well.
He's had to be really patient. He understands the situation and of course he's frustrated, he wants to play more minutes.
But I really value him. I'm really pleased to have him in the squad.
As we've seen, things can change really quickly with injuries or form, and he'll have a big part to play between now and the end of the season I'm sure."