The on-loan defender hopes to tie up a deal in January.
Agnew: “You can see immediately how committed Sean is towards doing well for the club. His preparation for every game is absolutely meticulous.
“He’s an intelligent footballer and we’ve already seen the benefits of that in his opening games.
“Obviously Sean has already made a big impact for us from set pieces. He’s got one goal and it would have been two but for his header at Reading going in off Leroy Lita.
“We knew that Reading would be vulnerable from corners and Sean was asking beforehand in which areas they might be at their weakest and where he should stand.
“We’ve been working on improving our output from set pieces and Sean will get his share of chances.
“People say that he’s only six foot, but it’s not just about height, it’s about judgement and it’s clear Sean is very good in the air.
“You have to be prepared to give new signings time to settle in at any club. They have to learn to gel with the players around them.
“But Sean has settled in really, really quickly. His partnership with David Wheater is already coming along well.
“You don’t know how players will react until you put them together but you can see that the partnership has promise because there’s a balance there.
“In any team it’s useful to have players with different qualities playing together.
“Boro had that in the past with Gareth Southgate and Ugo Ehiogu. We’ll get the same sort of thing from Wheater and St Ledger and it should get better as they continue to get used to each other.”