Mercedes has dominated the opening rounds of the 2019 Formula 1 world championship, securing five straight one-two finishes in the first five rounds.
Marko explained that the team's pace through slow corners at the Spanish Grand Prix was particularly dominant, and highlighted how worried they were about their chances at the Monaco Grand Prix.
"It was alarming how much faster Mercedes were in the slow corners, and Monte Carlo consists almost entirely of slow corners," Marko explained to Salzburger Nachrichten.
"We know where we are losing time. We are not generally slower, but we lose time in a few very specific, but just as significant, corners.
"When we were not nearly as dominant as them, there were two or three changes in the regulations each year to put us on hold. But nobody seems interested in that at the moment.
"We take a step forward, but Mercedes seemingly two. The basic direction is there, now we have to keep fighting.