Southampton are set to complete the signing of Celtic midfielder Stuart Armstrong, Press Association Sport understands.

After staving off relegation from the Premier League by the skin of their teeth, Mark Hughes’ men are on the brink of completing their first deal of the summer.

Scotland international Armstrong is moving to St Mary’s on what is understood to be a four-year contract, with the deal worth in the region of £7million.

Armstrong, 26, is understood to have completed his medical on the south coast on Monday and will become Hughes’ first signing since he replaced Mauricio Pellegrino in March.

After progressing through Dundee United’s youth system, Armstrong, who has made six senior appearances for Scotland, joined Celtic in 2015 and has helped the club win back-to-back domestic trebles.

He ended speculation over his future last summer when he signed a new two-year deal and scored 28 goals in a total of 145 appearances for the Glasgow club.

Southampton narrowly avoided the drop last season – they finished one place above the bottom three – after winning 1-0  at relegation rivals Swansea in their penultimate match.