Mercedes director of trackside engineering Andrew Shovlin has revealed the team is harbouring concerns about its ability to challenge Red Bull at the Spanish Grand Prix.
F1 returns to the Circuit de Barcelona-Catalunya this weekend as the more traditional European calendar gets underway.
Despite Lewis Hamilton taking victory in Bahrain, Mercedes struggled to match Red Bull on outright pace and had to rely on a brave strategy to fend off Max Verstappen.
With conditions in Spain likely to be closer to those of the season-opener compared to Imola and Portimão, Shovlin is expecting a difficult weekend for the championship leaders.
"We have got plenty on our list of things to worry about," warned Shovlin.
"It can be pretty hot there. It is a Tarmac that is now getting pretty aggressive and gives the tyres a tough time and we have just done two circuits that have been pretty cold and it has been fairly hard to get the tyres in the right window.
"Barcelona is a little bit more like Bahrain in the way that you are almost always overheating, and Bahrain was not a very kind place to us in some respects so that will be the main thing that we are worried about."
Despite his message of caution, Shovlin is wary of trying to forecast how the grid will fall into place across the weekend and revealed he is relishing the increased competition.
"To be honest, I think it will be a bit more of the same," he suggested. "You won't be able to split them, you won't be able to read the race and I think it will just be a bit tight and we are settling into that.
"I think the whole year is going to be like that and you just have to enjoy the competition, not let yourself get too stressed about it because it is going to be a long tough year."