Wanyama made his Celtic league debut in a 1–0 loss to St Johnstone on 21 August 2011. He played in central defence rather than his favoured central midfield role. He came on as a late substitute in a 4–0 win over Motherwell, and played for the whole second half in a 2–0 League Cup win over Ross County. On 29 September 2011, he started in Celtic's 1–1 draw with Italian team Udinese in the Europa League. This was his first European match for the club. On 10 December 2011, Wanyama scored his first goal for Celtic in a 1–0 win over Hearts at Celtic Park, a tremendous 25-yard strike which hit the top corner. His performances during December earned him the Scottish Premier League young player of the month award. He scored his second Celtic goal on 2 January 2012 in a 3–0 win against Dunfermline at East End Park. Wanyama scored in Celtic's 2–1 win against Dundee United at Celtic Park and in the 4–0 victory against Hearts at Tynecastle. On 20 October 2012, Wanyama scored twice against St Mirren at St Mirren Park, the second of which was a half volley from 25 yards out. On 25 October, Wanyama's agent released a statement saying that he had turned down an improved contract offer from Celtic, stating that his wage demands could not be met by the club amid speculation of interest from clubs in England. On 7 November, Wanyama opened the scoring with a powerful header as Celtic shocked Barcelona in the Champions League group stage, by beating them 2–1 at Celtic Park. Wanyama received a nomination for the PFA Scotland Young Player of the Year for 2012–13, but the winner was announced as Leigh Griffiths  After much speculation and a previous breakdown in talks, on 11 July 2013, Wanyama signed for Premier League side Southampton for a fee claimed to be £12.5 million, making him the first Kenyan to ever play in the Premier League. Wanyama said:   He made his debut on 17 August 2013, in a 1–0 away win against West Bromwich Albion. Wanyama made 24 appearances in his first season, but injuries hindered his efforts to make much of an impact in the team. Under new manager Ronald Koeman, Wanyama came into his own in the 2014–15 season. He scored his first goal for the club in a 1–0 league victory over Swansea City at the Liberty Stadium on 20 September 2014, after replacing James Ward-Prowse in the 69th minute.