TONY Mowbray claims Rhys Williams' new long-term contract is proof of Middlesbrough's ambition, but admits the club must continue to progress if they are to retain the Australian for the duration of his deal.

Williams signed a new four-and-a-half-year contract yesterday to commit himself to the Riverside until 2016 and draw a line under speculation linking him with a move to the Premier League.

Boro rebuffed a deadline-day offer from Bolton Wanderers last month, and Mowbray is confident the 23-year-old will not be going anywhere this summer, whether the Teessiders win promotion to the top-flight or not.

However, with the likes of Newcastle and West Brom also having scouted the Australia international extensively this season, the Boro boss accepts Williams will not be willing to put his Premier League ambitions on hold indefinitely if his current employers are unable to clamber out of the Championship.

"Rhys has signed this deal because he wants to be here and play for this club," said Mowbray. "He also wants to play in the Premier League, so we're hoping we can do that together.

"He's signed a four-and-a-half-year deal, so that doesn't mean that after half a year he's going to be allowed to leave. But between the two of us there will be an understanding that we have to keep showing progress and evidence that we're pushing on.

"We have to have the ambition to get to where he wants to be, and at the moment we absolutely have that. He's signed the deal because he knows we're a club that's ambitious to get back to the Premier League.

"Realism could hit hard if we don't achieve that in the next few years because if Rhys gets to two years left on his deal and we're still wallowing around in mid-table in the Championship, there's a fair chance he'll be looking at the situation closely if Premier League clubs come calling.

"But that's not in the forefront of our mind. We're focused on winning promotion and all being together in the Premier League."

With Barry Robson set to join Vancouver Whitecaps in the summer, retaining Williams' services is a major feather in Boro's cap.

The Australian joined the club's Rockliffe Park academy as a 16-year-old scholar and has rapidly progressed into one of the most highly-rated players in the whole of the Football League.

"Rhys is a player with lots of assets," said Mowbray. "He's six foot three, fast, can tackle and run all day, is a lovely passer of the ball and you forget that he's still just 23. He's a boy that still has lots to come and lots to learn.

"Hopefully, we will get the benefit of that improvement over the next few years and the quality he possesses will help our team get to where we want to go."

Williams will be in the starting line-up this evening as Boro travel to the New Den to take on a Millwall side that crashed out of the FA Cup at the hands of Bolton at the weekend.

Robson returns to the side after recovering from the wrist injury that has kept him out of the last three matches, but Nicky Bailey will not be risked despite returning to training last week."Nicky has had seven weeks off and he's only trained for four days," said Mowbray. "Even though he's looked very good in those four days, it's too big an ask to throw him in.

"I think there'll be a fair chance he'll have some part to play at the weekend (against Reading). We have to ease him in, but we're also mindful of the need to get him back up to full speed as quickly as we can."

Last February's game at Millwall was Boro's most controversial outing of the season with referee Chris Sarginson almost abandoning proceedings after a number of coins and bottles were thrown on to the field.

With his side struggling just two places above the relegation zone, Mowbray watched Leroy Lita's 83rd-minute winner secure a 3-2 success that underlined the strength of the spirit in the Teessiders' dressing room.

"It taught me a lot about my squad," said the Boro boss. "Days like that allow the team to grow together and aid the squad's mental development.

"The team learned a lot about itself that afternoon. As a manager, you try to pick a balanced squad. You want the trickery of someone like a (Merouane) Zemmama who can open the door to a goal, as he did last season, but you also need the fighting qualities of a Robson, (Matthew) Bates or Andrew Davies, as it was on that day.

"It's all about balance and coming out of the other end with the three points. That's what we'll be trying to achieve again."