Chelsea were left sweating on an injury to star summer signing Christopher Nkunku as they picked up a 1-1 draw with Borussia Dortmund last night. 

After falling behind in the 80th minute to an effort from Marius Wolf, Mason Burstow headed home an equaliser a minute from time in Chicago to open his account for the Blues.

But Chelsea fans were left fearing the worst when Nkunku, 25, went down clutching his leg with little more than 20 minutes on the clock and had to be replaced by Mykhailo Mudryk. 

Speaking after the game, which brought the curtain down on a successful tour of the United States, Pochettino said: "The doctors are checking him and I hope it is not a big issue. 

"He fell in the action, which was maybe a penalty, and he feels something in his knee but we hope it is nothing big.

"We hope he can be back quickly with the team. We need a few days to assess him."

Many supporters pointed the finger at the playing surface at Soldier Field but Pochettino was keen not to blame the conditions. 

He added: "We took some risks because the pitch is not perfect because the facilities are used for a different sport. 

"We won't blame the pitch for the injury. For me, it was bad luck."

Having seen his side beat Wrexham and Brighton before drawing with Newcastle, Chelsea went into the match with Dortmund having secured success in the first Premier League Summer Series by beating Fulham 2-0. 

But after a promising performance, the Blues fell behind when Wolf was deemed to be onside and swept home from close range. 

He threatened again soon after, only for Kepa Arrizabalaga to come to the rescue by pushing away the German international's low effort. 

And with full-time approaching, Burstow nodded home after a free-kick was kept alive in the penalty area.