Wolves Under 23s travel to the north east with nine points from eight games in 10th position.
The hosts are top of Premier League 2, Division 2 with 19 points from their eight games so far.
Sellars has been impressed with the attitude of his players and hopes that his players can learn from mistakes made against Fulham.
He said, “results are why we are in the game so you always dwell on that to an extent.
“After the game we said to the lads that we couldn’t fault their attitude or their football but we lost the game because we made individual mistakes and we also didn’t punish the opposition when we got in good situations.
“That’s something for them as players to reflect on as well as staff and to recognise that it’s something we’ve got to improve on.
“We’ve watched it back and we’ve done a post-match analysis as a group in terms of performance - I thought in both boxes we didn’t do great.
“We got into some really good situations with the ball, we realised that the quality of our crossing wasn’t quite good enough but we also didn’t get enough bodies in the box and that was a negative.
“When the balls did get into the box, we were getting out numbered - even if we didn’t win the first one, when the second ball was dropping we weren’t there either.
“That was something that we worked on a little bit this week - we’ve looked at the quality of the crossing and getting balls into the box.”
Despite Middlesbrough being top of the table, Sellars isn’t phased by facing the league leaders.
Boosted by the addition of a number of first team players to his squad, he says it’s a chance for his side to bounce back from two defeats.
“Middlesbrough are top of the league - we’ve watched a little bit of them and they look a hard-working team with some quality.
“Again, they look like they’ve got goals in them as well so we’re in for a game but that’s the challenge and it’s a chance for us to bounce back from Monday night.
“Having a game on a Sunday means we’ve got one less day for recovery but it shouldn’t be a problem for the boys at this age.
“We’ve moved everything a day forward in terms of what we try to do but we’ve got enough time to focus and prepare for the game,” Sellars said.
“We’ve got some first team players in the squad - Connor Ronan is back for the game, Michal Zyro, Prince (Oniangue) and Sylvain (Deslandes).
“From that point of view, it means that the work we’ve done on Friday and Saturday builds up some more understanding between the players.
“The game’s at the Riverside Stadium against Middlesbrough so I’m hoping the first team players will respond to that as well as the young players looking forward to the game.”
Sunday’s game will be too soon for the return of Sherwin Seedorf who missed Monday’s game through injury.
The Under 23s coach is disappointed not to have Seedorf available but says it’s a chance for someone else to take their opportunity.
He said, “Sherwin’s (Seedorf) still got a tight glut and obviously because his game is based around speed, we’re a little bit mindful of that so we’ll protect him a little bit.
“He’s still a long boy developing so we’ll be patient with him and he’ll probably start training again next week.
“That’s disappointing because he was doing really well - he’s made a really big impact over the past few weeks but again it’s an opportunity for someone else."
