Heikki Kovalainen is to replace fellow Finn Kimi Raikkonen for the final two rounds of the 2013 F1 season after Lotus officially announced the signing of the 32-year-old.

Raikkonen had been due to conclude the season with the Enstone-based team despite his recent contractual issues but was forced to stand down from the races in the United States and Brazil to undergo surgery on his injured back.

Kovalainen, Nico Hulkenberg, test driver Davide Valsecchi and - most surprisingly - Michael Schumacher were all linked to the drive for the final two races of the season, with the team agreeing terms with Caterham to allow Kovalainen to return to a race seat for the first time since the 2012 season finale.

He had been spending the current campaign as test and reserve driver with the Leafield-based team having been replaced in its race line-up for 2013.

"It is a fantastic opportunity for me to join Lotus F1 Team for the final two races of 2013," he said. "We've seen this year that the E21 is a car which can win races and finish on the podium, so I will be pushing hard for the best results possible.

"Jumping into a car so late in the year when you have not been competing in the races all season will be a challenge, but I know the team at Enstone well so I have no concerns about getting up to speed. This is a great opportunity for me, so I would like to thank Tony Fernandes and Caterham F1 Team for allowing me to take advantage of it."

Reflecting on the announcement, team boss Eric Boullier admitted it had been a difficult decision not to promote GP2 title winner Valsecchi into a race seat but said the tight nature of the constructors' championship battle had led to it ultimately going with the experience of a driver who has already raced in F1.

"Obviously we had to move quickly following the news of Kimi's non-participation in the final two races of this season, and we found ourselves facing a difficult decision in terms of who should take the wheel in Austin and S?o Paulo," he said. "On the one hand we had our reserve driver Davide Valsecchi - who is a talented young driver that has shown a great deal of promise - and on the other we had the opportunity to bring in a seasoned Formula 1 competitor in Heikki.

"Whilst we have every faith in Davide's abilities, we are obviously involved in a tight Constructors' Championship battle, so it was decided that the experience Heikki could bring to the team would be invaluable as we aim to finish the year in the best position possible. We must thank Tony Fernandes and Caterham F1 Team for their professional conduct in allowing Heikki to join us for the final races of this season."

Caterham team principal Cyril Abiteboul added: "We were asked by Lotus F1 Team if we could release Heikki from his contract with us for the final two races of 2013 and we are pleased that we can help to give him the chance to race again in 2013. He is a valued member of the Caterham family and we're sure that he'll do a good job in the USA and Brazil."

Both Hulkenberg and Schumacher meanwhile are reported to have turned down the chance to take up the role.