NEIL WARNOCK cast further doubt on the future of Britt Assombalonga, as Middlesbrough's stuttering play-off hopes suffered a significant blow with a 1-0 defeat at Millwall.

The Congolese forward, who is Boro's £15m record signing, did not make the bench at the Den, despite being declared fit.

His absence was made even starker with a woeful attacking display in south London.

After Marcus Tavernier pulled up just before half-time, the Boro manager made three further tactical substitutions after the break.

A first half own-goal by Grant Hall summed up a tepid afternoon with few chances on goal.

Warnock defended leaving out Assombalonga, who is set to see his contract expire later this summer, but also took aim at his strikers.

He said: “Britt is fit, but I thought it was time to give Josh Coburn a bit of experience away from home.

“I was going to put Ashley Fletcher on before him at the moment, so he was fit to be selected today.

“I thought our wide players and strikers could get at them today, so it shows what I know.

“I think some of the lads might not want to compete against a tough, physical Millwall side.

“And I think today just magnified what we’ve got to look for next season. We’ve known all along – it was like playing with eight men at times today.

“Next season, we should have 11 and I look forward to it.

“We won’t chuck the towel in now, but the first half today was just unacceptable. I’m 72, and I could have put more effort in today.”

The game was a disappointing end to a run that saw two straight victories.

Three changes were made to the side that won against Preston earlier in the week, with Djed Spence, Tavernier – who netted at the Riverside – and Marvin Johnson coming in.

The hosts made an equal number of switches from their QPR horror show, where they lost after going two goals ahead, with Murray Wallace, Danny McNamara and Billy Mitchell starting.

Although Boro took the initiative early on, the game became one where the battles were mostly fought in midfield.

Millwall started to press though, and the visiting defence was showing signs of being tested.

The first proper effort of the game fell on 27 minutes to the hosts. Jed Wallace picked up a ball from Mason Bennett, and showed his pace to trouble the Middlesbrough defence.

Marcus Bettinelli prevented the Millwall striker from netting his second goal in as many games though, as he tipped his effort behind the post with a low dive.

If the effort was a warning shot for Boro, they were finally undone just after the half-hour mark.

Buoyed by his effort minutes earlier, the 26-year old winger once again showed his speed, this time down the left-hand flank

Jonny Howson found himself beaten for pace, allowing Wallace to deliver the ball quickly into the centre.

Hall found himself in the wrong position at the worst possible time, and was unable to do anything except turn the ball past Bettinelli into his own net.

Instead of a response by Middlesbrough, it could have been even worse five minutes before the break. Wallace again tormented the visitors, this time splitting the Boro defence to let in Danny McNamara unchallenged, with a good sight on goal.

It was somewhat fortunate that the full-back may have had too much time and space to place his effort, as he directed his strike just wide.

The first Middlesbrough attack came just before the interval, when Yannick Bolasie failed to properly connect to a Johnson cut-back.

In a further blow to Boro, Tavernier was injured before the break, and was replaced by ex-Millwall player George Saville.

Warnock made three more substitutions after the restart - Nathaniel Mendez-Laing, Fletcher and Duncan Watmore replacing Spence, Bolase and Chuba Akpom.

The changes appeared to rejuvenate a previously flat Middlesbrough side, and Saville made Bartosz Bialkowski save with his feet five minutes after the restart.

It was a much hungrier display from the visitors, although they still failed to properly trouble the Millwall goal.

Paddy McNair was able to get a shot on target in after 77 minutes, but his effort was aimed straight at Bialkowski.

Although Millwall were less attack-minded during the second half, they could have put the game out of reach a minute later.

A sweeping counter-attack found Jon Dadi Bodvarsson in the area, but Bettinelli was able to tip a shot by the Icelandic international over the bar.

It proved to be the final meaningful action of an afternoon that disappointed in so many ways for Middlesbrough.

The visitors will now have to wait until Good Friday to respond to the loss, when they travel to Jonathan Woodgate's Bournemouth.

Defeat at Millwall puts a dent in the push for the play-offs, although Boro could have few complaints.