Chelsea manager Thomas Tuchel has sought to explain Saul Niguez's half-time substitution during the Blues' 2-1 win away at Watford on Wednesday night.
The match at Vicarage Road was halted in the 13th minute for half an hour as a fan received medical attention after he suffered a cardiac arrest.
The Blues took the lead on the half-hour mark after the match resumed, but were pegged back just before the break with a Dennis Emmanuel goal.
They seemed to have been troubling the Blues, and Thomas Tuchel responded by hurling off the Spaniard, who has featured in just a couple of matches.
"He was on a yellow card. We had two options, [the other was to] take Marcos off and put Saul as a wing-back. I had this in my mind before the game if something happened to Marcos, but it wasn’t the right match to try new positions,"
"It was him [who went off] to change the shape a little bit and have Thiago on the pitch with the quality of organising, and Trevoh in the six who is more physical. Unfortunately, Trevoh injured himself so we ended up with Ruben in the single six. It was a tactical decision and we go on from here,"
Eventually, it was Hakim Ziyech who stepped off the bench to score the winner in the 73rd minute, which ensured the Blues stayed top despite Liverpool and Man City winning their respective matches.
Up next for the Blues in the Premier League is a London derby at West Ham on Saturday afternoon.