The Spanish driver went straight to the point, directing his plaints towards McLaren partner Honda.
“We have only one problem, that is the power unit!” said Alonso.
“There is no reliability and there is no power. I think we are 30kph down in the straight, every straight.
"When you are 30kph down in every straight it’s difficult also to have a feeling on the car. Everything feels good but when you arrive to normal speed you don’t know what is going to happen."
Alonso said the team's plight was at throwback to its state of affairs twelve months ago.
"Probably this year it’s a little bit more frustrating because the change of regulations and things like that, you have higher hopes.
"You think that you can close the gap over the winter so definitely we need to improve and we must improve. The situation is far from ideal."
Alonso invoked a bit of mitigated circumstances, as the troubles are effecting the team now, and not during the course of a Grand Prix weekend.
“We are not matching our expectations and we are not as fast as we want to be in this winter testing. On the other hand it’s only winter testing.
"I remember 2014, Red Bull were doing like seven laps in winter testing and won two or three grands prix that year. So let’s say that the season is long enough that you can have time to react."
Still, the frustration - and annoyance - in the McLaren camp is now in overflow mode.
"I'm driving at my best. I feel I am the best driver out there, I just need an engine that can run as quick as the others on the straight.
"We cannot pretend that we are happy and everything is going OK. We are not completing our programme, we are not doing the laps we plan every morning. We are missing some information.
"With the lack of laps there are always some items that they go through to the next day. The next day we cannot complete the programme, then go to the next day.
"And now there are only two days left, one for each driver. So definitely a little bit behind schedule in terms of reliability and in terms of performance. But this is winter testing and it’s what it’s all about."