Daniel Ricciardo endured what he has described as a "disrupted day" of practice for the Russian Grand Prix after McLaren was forced to change his power unit ahead of FP2.
The team found an issue between sessions on the unit used in FP1 and had to swap, although no penalty was taken as the replacement was already in the allocated pool of engines, and with a fix assured for the original system.
Ricciardo missed almost half of the second session and was then hampered by a red-flag period triggered by Antonio Giovinazzi's crash towards the end of the hour.
"It is one of those things but it certainly affected it and then we got caught with yellows, reds and people on high fuel at the end," said Ricciardo.
"Not a great day but luckily it is just practice today but it was certainly a disrupted day."
Ricciardo ruing rain threat
Ricciardo's struggles were amplified by the threat of a washout on Saturday with heavy rainfall predicted.
Asked if there was any jeopardy of losing qualifying, Ricciardo replied: "I think for tomorrow there is, it is no secret.
"The rain they are predicting is a lot - a lot! I think in Spa, it was on a Sunday. For whatever reason... we have done it before with Japan 2019, we qualified and raced on a Sunday so it can be done.
"I am, let's say, optimistic for Sunday but tomorrow, I don't want to say there will be a change of schedule but it is not unlikely."
Ricciardo hoping not to "encounter" Verstappen
Max Verstappen will start at the back of the grid for the grand prix after taking a complete power unit change between sessions.
Asked if this opened the door for another shot at victory, Italian GP winner Ricciardo responded: "I think after today, I don't really know about performance and where we are at so probably a lot to process at the moment.
"If he is starting at the back, I would like to think we don't encounter him during the race but I honestly don't know yet, we will see."