Under-21s coach Graeme Lee was delighted with the contribution of Rhys Williams after the defender played 90 minutes of Boro's 3-2 defeat to Reading on Wednesday.
Williams made his first appearance for almost a year having gone through rehab for an Achilles injury he sustained at Barnsley in January.
However, the Australian returned to action on Wednesday and Lee praised Williams' attitude and performance against the Royals.
"We were speaking to him 15 minutes before the end to make sure he was ok," said Lee.
"Obviously we wanted to win the game, but when a player has gone through what Rhys has you've got to put the player first.
"He got through the 90 minutes which we were delighted with. It's been a long road back for him but he's put a lot of hard work in, has done well and performed well.
"He stepped on the pitch confident with no hesitation going into tackles and jumping for headers - you can't fault him.
"We're delighted to have him back and see him getting 90 minutes, and no doubt the first team will be, too."
The result against Reading condemned Boro to three successive defeats and means the Teessiders are now eighth in the Barclays Under-21s Premier League table.
Graeme Lee had no complaints about the result, though, and says the Under-21s must recover the form they showed earlier in the season.
He said: "To be honest be probably didn't deserve to get anything out of the game but then you go and score two goals.
"Arnel's finishing in training is unbelievable and he's gone and scored two there. The lads got belief then and we might've scraped a point.
"But it was frustrating to watch. We started alright but conceded some silly goals, they took over the game and we couldn't get a grip until we got the goal.
"You can't wait until you get a goal until you kick-start - you've got to be at it from the beginning.
"We've lost three games on the bounce now and that's not us.
"We've got to make sure we get back to how we were and that's starting games in the right way and in an aggressive way."