He arrived on crutches but is now the crutch around which Pep Guardiola is building his Manchester City side.

Ilkay Gundogan was the difference as City beat Barcelona at the sixth time of asking on Tuesday night. Two goals in a 3-1 victory capped a performance of energy, aggression and invention. Yaya who?

Indeed, City appear to have finally found a midfielder who marries craft, graft and goals. The engine of Toure, the subtlety of David Silva and the instincts of Kevin De Bruyne; Gundogan has the lot.

Ilkay Gundogan celebrates scoring in Manchester City's 3-1 win over Barcelona

Gundogan scored twice and Kevin De Bruyne got the other as Man City won

And to think he cost only £21million from Borussia Dortmund back in June. It was a transfer which slipped under the radar given his injury and the impending European Championship.

He took a tour of the club’s training ground wearing a brace on his right knee and, dressed in cut-off jeans, leather jacket and baseball cap, he looked more like a member of a backstreet dance troupe than he did Premier League footballer.

But footballer he most certainly is, and a fine one at that. At £21m he could well prove the signing of the season. To give that fee some context, Paul Pogba’s agent Mino Raiola received £24m for his part in taking his client to Manchester United.

Gundogan has five goals from nine starts having recovered from that serious knee injury to make his debut in mid September. World-record £89m Pogba, by comparison, has three from 13 appearances.

Gundogan covered a lot of the central areas on the pitch against Barcelona

GUNDOGAN SEASON STATS Premier League games: 6 Premier League goals: 3 Champions League games: 4 Champions League goals: 2 TOTAL GAMES: 10 TOTAL GOALS: 5 Advertisement

It may have been lost amid the euphoria of his second against Barca, but it was Gundogan who started the move as he nicked possession on the edge of his own box.

Motoring forward, he checked his run entering the penalty area and got his reward as he steered home the rebound after Jesus Navas’ cross deflected off Sergio Aguero.

He made it look simple, as he had done in the first half when arriving unmarked at the far post to meet Raheem Sterling’s pass and fire City level following Lionel Messi’s opener.

Gundogan celebrates City's win with team-mate Leroy Sane in the changing room

Manchester City players and staff celebrate in the dressing room after the victory

But his game was about so much more than his cunning double strike.

Of his 28 passes, every one attempted in the Barca half found its target. The stats men will also tell you that he won five ‘duels’ and made six ‘recoveries’.

This performance, however, should have come as no surprise, especially as, just four days earlier, he scored twice in the 4-0 demolition of West Brom.

After that match, Guardiola spoke of the 26-year-old’s importance.

‘I said to him, “thank you”,’ revealed the Spanish boss.

‘We need him. Without him we cannot achieve our target, it is impossible.’

Gundogan was injured and on crutches when he signed for Manchester City

Guardiola has not felt so moved to champion any others in such glowing terms. In the Bundesliga he watched Gundogan act at the heartbeat of Jurgen Klopp’s Dortmund side and had coveted him ever since.

Thankfully, for City, it was to Manchester and not Munich that he eventually took the Germany international.

Upon arriving, Gundogan said: ‘The reason for my transfer is the great opportunity to join Pep Guardiola and Manchester City.

‘Guardiola asked me to go to Manchester and convinced me with his philosophy. I believe this is the right step for me at the moment. Under his lead I want to keep on improving my skill as a football player.’

Gundogan's goals helped Manchester City win and keep their Champions League dreams alive

Agent Mino Raiola earned £24 for his part in Paul Pogba's move to Manchester United - more than Manchester City paid for Gundogan

And improve is all Gundogan has done since signing for Dortmund for £3m from Nurnberg in 2011. He won the title in his first season with Klopp hailing his 'intelligence' and 'willingness to learn'.

His profile rocketed during the run which took Dortmund to the final of the Champions League in the following season, his dominance in the semi-final victory over Real Madrid winning particular praise before he scored from the penalty spot in the 2-1 defeat to Bayern Munich at Wembley in the final.

A back injury, though, was to rule him out for the entirety of the next campaign. Questions were asked over his ability to recover and eyebrows were raised even further when City invested in a player sidelined with a dislocated knee.