Christian Pulisic admitted to being "very frustrated" at being left out of Chelsea's starting line-up for Wednesday's Champions League semi-final second leg with Real Madrid.

The United States international scored a crucial away goal for the Blues in last week's first leg but was named among the substitutes for the return fixture at Stamford Bridge.

He again made his impact known, however, by setting up a goal for Mason Mount 18 minutes after being introduced from the bench in the 2-0 win, which saw Chelsea through 3-1 on aggregate.

"I'm very frustrated," Pulisic, who has struggled with injuries this term, told CBS Sports. "There's not much else to say. I wanted to play from the beginning, as I always do.

"I've had to continue to prove myself over and over again. But, as always I reach out to God and he gives me strength. With that behind me, nothing can stop me really."

A look at the Opta stats shows Pulisic has a right to be frustrated, having now scored and assisted a combined four goals in the Champions League in nine appearances this term.

Only Olivier Giroud and Timo Werner have been directly involved in more (both six) - in eight and 11 games respectively.

For comparison, Mount - who has been superb for Chelsea this season - has three direct goal involvements in 10 Champions League games, while Kai Havertz has two from 11 respectively.

Focusing on the Premier League, meanwhile, Pulisic has four goals and one assist in 23 appearances this term, just 14 of those being starts.

Pulisic's average of a 0.26 goals per 90 minutes is slightly better than Havertz's return of 0.25 and behind only Giroud (0.5) and Tammy Abraham (0.52) among Chelsea's attackers. Werner, for context, averages 0.23.

The 22-year-old also performs better when it comes to chances created per 90 minutes in the English top flight when compared to Havertz - 1.37 to the German's 1.07.

But Pulisic still ranks some way below Hakim Ziyech, who has created 2.54 chances per 90 minutes this season and will also perhaps feel that he should be starting more often.

Mount (2.68) and Callum Hudson-Odoi (2.71) lead that particular metric, incidentally, which only highlights just how many options Thomas Tuchel has available in that zone.

One area Pulisic struggles in comparison to his attacking rivals is passing accuracy in the opposition half - 80.95, which is lower than Havertz's 84.3, Mount's 85.45 and Hudson-Odoi's 85.65. ​

The American's win rate when starting games also does not make for good reading.

The Blues have won 13 and lost just two of the 20 league games Pulisic has not featured from the beginning this term, compared to four wins and five losses in the 14 games he has been included in the XI.

Chelsea average 1.8 league goals with Pulisic in their starting line-up, as opposed to 1.3 without, while their average goals against rises from 0.6 to 1.4 when he starts.

Tuchel ultimately knows best when it comes to his team selection - and he is backed up by the possibility of a Champions League and FA Cup double - so Pulisic will simply have to keep proving himself if he is to hold down a regular starting spot.