Oxford United have completed the signing of Cambridge left back Anthony Tonkin, but also released Chris Carruthers and Marcus Kelly – and central defender Luke Foster could be on his way too.

Tonkin, 29, who has played for Yeovil, Stockport, Crewe and Forest Green, has signed for a small fee, funded by the 12th Man scheme, in a deal that keeps him at Oxford until 2012.

United manager Chris Wilder said: “I believe he’s been the best left back in our division for a while.”

Foster, player of the year and supporters’player of the year in 2008, has been given permission to talk to other clubs, and could make the journey in the opposite direction – to Cambridge.

“We brought in Jake Wright last week, and following that, Cambridge made an inquiry about Fozzie,” Wilder said.

“We had a meeting in which we discussed his future and I told Luke that we wouldn’t be offering him a contract at the end of the season.”

Former Lincoln City player Foster was signed by the U’s from Stalybridge in February 2007, quickly becoming an instant hit with the fans and an almostever-present in the back four. However, the capture of Tonkin and Wright means his place in under threat.

Cornish-born Tonkin made around 100 appearances for his first club Yeovil before a £50,000 move to Stockport, followed by a £150,000 move a year later to Crewe.

In total, he has made around 350 league and cup appearances, a great many in the Football League.

Tonkin said: “I’m delighted to join Oxford. It’s a massive club that shouldn’t be in this league and it’s a great opportunity for me to push on and get where I want to be, and where this club wants to be, which is back in the Football League.”

With Kinniburgh injured, Tonkin will effectively replace another left back, Chris Carruthers, who was on high wages by Conference standards.

Carruthers and Kelly have spent recent months on loan at York City and Kettering Town respectively, and with the January transfer window now open, an agreement has been reached to allow both players to find new clubs.

Carruthers joined Oxford in the summer of 2008 on a free transfer from Bristol Rovers and made 35 appearances before moving to Crawley on loan in September, and then joined York on loan on his return.

Kelly came to United from Rushden but made just one start and two sub appearances before moving on loan to Kettering in November.