Jonny Williams was forced off just before half-time with what appeared to be a recurrence of his groin injury as Town’s U21s lost 3-2 to Bristol City at Playford Road having been 2-0 in front at the break.
Monty Patterson put the Blues in front in the 27th minute, then Kyle Hammond made it 2-0 three minutes later as Town dominated the first half.
However, the visitors fought back and claimed an unlikely win via goals from Marley Bishop on 63 and 74 and sub Matt Long in the final moments.
Williams, Kevin Bru and Darren Ambrose all started for a strong U21s side, alongside trialist striker Daniel Akindayini.
The 19-year-old striker is with Tottenham’s youth system, where Bryan Klug, Town’s academy director previously worked. He has scored four goals in 19 appearances for Spurs’ U21s this season, while he netted 15 goals in 27 appearances for their U18s last year.
Facing a much less experienced side, the Blues began on top and Akindayini shot into the side-netting after seven minutes.
Ten minutes later, Ambrose curled a freekick over as the Blues were unable to make their early dominance tell.
But on 27 they finally took the lead when impressive left-back Myles Kenlock cut his way through the Robins midfield before teeing-up Patterson 25 yards out and the New Zealand U20 international struck a low shot into the corner of the net giving Bristol City keeper David Richards no chance.
Town were close to making it 2-0 within a minute, Matt Clarke rising highest at a corner but saw his header nodded off the line by Lewis Hall.
However, a second Blues goal took only another two minutes, Alex Henshall crossing from the left and Hammond nodding home at the far post.
A minute before the break on-loan Crystal Palace midfielder Williams limped off holding the groin which has caused him so much trouble since he was injured in the Watford home game in November.
The Wales international, who was replaced by Cemal Ramadan, went straight to the dressing room and the severity of the problem will now be assessed.
Just before the break, Ambrose, who alongside Bru had controlled the game for the Blues, saw another freekick from just outside the area saved.
The Robins weren’t far away from an equaliser three minutes after the restart, Bishop - who Town showed interest in when a schoolboy - getting beyond keeper Michael Crowe after he had rushed off his line before shooting wide.
Bru hit the next in a succession of Town freekicks around the area into the wall on 58, before Henshall did well to work himself space on the left of the box but poked his shot over.
On 62 Kundai Benyu replaced Patterson, the goalscorer having suffered what appeared to be an ankle injury a few minutes earlier.
A minute later, with the Blues still very much on top, the visitors pulled a goal back. Henshall lost possession, the Robins broke and Bishop shot past Crowe and into the net off the post.
Ramadan, who had looked lively since coming on, hit a dangerous shot on the turn from inside the area which Richards did well to save low to his left.
Ambrose saw yet another freekick saved on 67, then Henshall’s dangerous cross from the left was bundled out of play at the near post by a defender. The winger then saw a low shot tipped wide by the Robins’ keeper.
Town were made to rue their missed opportunities on 74 when Ben Withey played a long ball forward and Bishop got in ahead of Joe Robinson to equalise.
Clarke headed wide from Henshall’s freekick with five minutes remaining as the Blues looked to restore their lead.
Town ought to have scored their third in the 87th minute when Henshall cut the ball back across from the left but Akindayini blazed over from 10 yards.
Jamie Morgan forced Crowe to save his low shot past his right post close to the end and from the resultant corner the visitors grabbed a win which had hardly seemed on the cards.
Jack Batten nodded the deep flag-kick down into the six-yard area and Long stabbed into the roof of the net from a few feet out.
It was a game Town should never have lost having been 2-0 up after a first half which they dominated.
But City defended stoutly and grabbed their chances when they came, whereas the Blues were unable to create too many clear-cut opportunities, particularly in the second half, and failed to make the most of numerous set pieces.
While the watching Mick McCarthy and Terry Connor will be concerned by Williams’s injury - the midfielder had a few lively moments before he went off without ever looking quite at his best - they’ll be delighted to have seen Bru and Ambrose come through the full 90 minutes after their recent spells out of action.
U21s: Crowe, Hammond, Kenlock, Bru, Robinson, Clarke, Patterson (Benyu 62), Ambrose, Akindayini, Williams (Ramadan 44), Henshall. Unused: McDermid, Fowler, Guldbrandsen.
Bristol City: Richards, Withey, Hall, Vyner, Batten, Murphy, Morgan, Gilabert (Harper 75), Andrews, Bishop (Difford 78), Hunter (Long 62). Unused: Wollacott.