Raikkonen worried about Mercedes form

The Finn returned to work on Thursday, driving for the first time since the 2005 season ended more than 100 days ago.

Raikkonen joined his team at the Barcelona circuit and took to the track with the new MP4-21 car, which was unveiled last Monday.

The McLaren driver, however, did not enjoy a good day, spending a lot of time in the pits and finishing as 12th quickest.

The team's test driver Pedro de la Rosa finished at the bottom of the times after suffering an engine blow-up.

"It is the first time I was driving, and it was okay, but we still have work to do," Raikkonen told autosport.com at the end of the day.

"I was expecting nothing before I came, so I knew we have issues with certain stuff, but we are going to get there and there is going to be some improvement.

"The biggest part of the problem is the engine, but like I said, things are happening so in the coming weeks we will improve it."

When asked how many races will McLaren need to be more competitive, Raikkonen said: "I do not know, you ask Mercedes.

"They are not where they should be and they need to improve. On the engine side we have a lot of work to do."

Although Raikkonen admitted he was worried about their form, last year's runner-up was hoping the team would be able to make progress before the start of the season.

"We have been testing for a long time but we have not been able to make progress," he added. "It [the engine] is definitely our weakest link now, but improvement is coming.

"It is the first time I am in the car. I know there is a lot of work to do but they are improving, and I know what is coming. I am slightly worried but not too much. Sure I can expect more but now we'll wait for a proper engine and we'll see."

Despite the problems, however, Raikkonen was happy to finally return to work.

"It's nice to come back but of course when you come back you would rather see yourself fast, but it is always nice to come back."