Steve Bruce last night launched a withering attack on Darren Bent, accusing the striker of being a “massive let down” following his club-record £24m move to Aston Villa.

Bent signed a four-and-a-half-year contract worth around £80,000-a-week at Villa Park last night, after two days of hectic negotiations that followed the submission of a formal transfer request on Sunday evening.

The striker's departure has caused considerable consternation among the Sunderland hierarchy, who feel betrayed by Bent's lack of loyalty despite the Black Cats effectively plucking him from the wilderness of Tottenham's reserves when he made a £10m move to Wearside 18 months ago.

Sunderland officials will spend the rest of the week scouring Europe for a short-term replacement, with the repercussions of Bent's departure having been exacerbated by an injury to Danny Welbeck that requires exploratory surgery that could keep the youngster sidelined for up to six weeks.

However, the overriding feeling last night was one of dismay at the unseemly manner of Bent's exit.

“It's hugely disappointing that Darren has decided that his future lies away from Sunderland and the players, our supporters and the club as a whole have every right to feel massively let down,” said a clearly seething Bruce.

“The timing is especially hard to take, given that we are progressing positively and are in a great position to push on.

“Everyone has been nothing but supportive of Darren in his time at Sunderland, but its obvious he's not been himself in training and we've certainly not seen the best of him in games in recent weeks - and we now understand why.

“I've always stated that my aim is to build a talented, young squad for the long term to help the club achieve sustained success and I want Sunderland fans to know that our ambitions haven't changed on that front.”

Bent, who was formally introduced as a Villa player at a 7pm press conference at Villa Park last night, has denied suggestions that money was the primary motivation behind his move.

The 26-year-old, who claimed he only became aware of Villa's interest in the wake of Sunday's Wear-Tyne derby, also refuted suggestions that he had been unsettled at the Stadium of Light for the majority of the season.

“I had some good times at Sunderland, but that's all behind me now,” said Bent. “I'm looking forward to getting going with Aston Villa. It's a new challenge for me and something I want to be part of.

“I'm sure Steve Bruce is disappointed, I'm sure the fans and the whole club are disappointed as well. I'm sorry it's ended the way it has, but I'm looking forward to my time at Aston Villa now.

“I wouldn't say my head was turned, but as soon as I was made aware that I could join Aston Villa, it was something I wanted to do.

“I'm sure they (Sunderland) are not happy with the way it went, but hopefully I gave them 18 good months there and scored a lot of goals. Everyone will have different opinions of why I've come to Aston Villa, but I could have gone to West Ham (for a lot of money) when I left Charlton, but I didn't. I chose Spurs for footballing reasons and the same applies here.”

Bent's departure has left Sunderland in a difficult position just 12 days before the transfer window swings shut.

On the one hand, the Black Cats are aware of the urgent need to recruit an attacking reinforcement given the likely unavailability of Welbeck and Fraizer Campbell for more than a month. Welbeck will have exploratory surgery on a knee problem that has troubled him for a number of weeks on Tuesday.

However, having held preliminary discussions with a number of Premier League clubs on Monday night, chairman Niall Quinn is only too aware of the difficulty of making a permanent signing during the January window.

Sunderland were quoted unrealistic prices for a range of targets that are understood to have included Tottenham duo Peter Crouch and Roman Pavlyuchenko and Manchester City's Emmanuel Adebayor. There has also been contact with Cardiff City over England international Jay Bothroyd.

With the likelihood of a permanent replacement for Bent receding, Bruce has turned his attention to the European market and instructed his scouts to deliver immediate reports on players who may be available on a short-term basis.

While Sunderland cannot loan a player from a Premier League club unless either Welbeck or Nedum Onuoha is signed permanently this month, they are permitted to make a short-term signing from abroad.

Talks are planned with both Paris St Germain attacking midfielder Stephane Sessegnon and Inter Milan's Sulley Muntari, but neither is a like-for-like replacement for Bent, and even if both were to arrive on Wearside this month, a third addition would still be required.

Luis Suarez has been on Sunderland's radar for some time, but the Ajax striker is close to joining Liverpool as a replacement for Ryan Babel, who completed a move to German side Hoffenheim yesterday. Hoffenheim striker Demba Ba could be an alternative target, despite having failed a medical ahead of a proposed move to Stoke City this week.

Meanwhile, Preston boss Phil Brown is hoping to take Sunderland midfielder Jack Colback on loan for the remainder of the season.