Celtic sign Stuart Armstrong & Gary Mackay-Steven

Stuart Armstrong in action for Dundee United in their League Cup semifinal win over Aberdeen. Picture: SNS

The Scottish champions had appeared set to be frustrated in their efforts to secure 22-year-old midfielder Armstrong, having had two previous offers for the player rejected by United chairman Stephen Thompson earlier in the January transfer window. But, just a few hours before last night’s midnight deadline, Celtic were successful with an offer believed to comprise a fee of £1.6 million and a sizeable sell-on clause. Armstrong, who was under contract at Tannadice until 2016, had also been wanted by Burnley but the English Premier League club were not interested at that price.

Celtic also persuaded United to part company with Mackay-Steven, having previously signed a pre-contract agreement with the 24-year-old winger for a move at the end of the season. A fee of around £250,000 secured his immediate recruitment.

Armstrong and Mackay-Steven travelled to Glasgow for medicals and discuss personal terms, with Celtic optimistic of completing the necessary paperwork in time.

The deals are profitable for United but will be met with dismay by fans as manager Jackie McNamara loses two of his most talented and influential players at a key stage of a promising season. Armstrong and Mackay-Steven both shone at Hampden on Saturday as United defeated Aberdeen 2-1 to reach the League Cup final where they will face Celtic on 15 March.

United last night tried to re-inforce their squad when they offered Hibs £150,000 for their former midfielder Scott Allan. But the Easter Road club rejected the bid and were understood to be determined to hold on to Allan, who has been a stand-out performer this season. United were successful with another move for an ex-player, bringing left-back Paul Dixon back to the club from Huddersfield Town.

Hibs also captured the signing of former Aberdeen youngster Fraser Fyvie last night. Fyvie was released by Wigan earlier in the day.

Celtic’s capture of Armstrong and Mackay-Steven provides manager Ronny Deila with a significant boost ahead of the final four months of a season in which he has made plain his ambition to win the domestic treble at his first attempt.

Armstrong was named Young Player of the Year by the Scottish Football Writers’ Association in 2013. He made 150 appearances for United and scored 22 goals.

Mackay-Steven, who joined United from Airdrie United in 2011 after earlier being released from Liverpool’s academy as a teenager, has been capped once for Scotland so far, as a substitute in the Hampden friendly against USA in November 2013.

Both Armstrong and Mackay-Steven are cup-tied domestically and will not feature in Celtic’s remaining League Cup and Scottish Cup matches. But one of them will be eligible to be added to Celtic’s squad for the Europa League last-32 tie against Inter Milan later this month.

Celtic were also being linked with a move for 18-year-old Kilmarnock striker Robbie Muirhead last night. Earlier in the day, they completed the signing of Northern Ireland under-21 international winger Michael Duffy from Derry City for a fee in the region of £150,000.

The 20-year-old, who had an impressive trial period at Lennoxtown in December, is initially expected to be part of Celtic’s development squad.

Celtic also announced that 19-year-old Irish central defender Eoghan O’Connell had agreed a two-year contract extension which commits him to the club until 2017.

Meanwhile, Manchester United midfielder Darren Fletcher was on the brink of a move to West Bromwich Albion last night after a lack of games under Louis van Gaal at Old Trafford this season.