MANCHESTER City's Zack Steffen has undergone knee surgery after his Middlesbrough loan move came to an end - adding a layer of complication as the keeper ponders his next move.

According to reports in his homeland, the USA international could be out of action for up to four months.

On the back of a full season of regular football, Steffen revealed earlier this year that he doesn't intend to return to Manchester City this summer.

Whether he leaves the Etihad on a permanent deal or another loan is not yet clear, but Steffen's immediate priority is recovering from the surgery on a knee problem that troubled him throughout his time at Boro.

Steffen missed a spell of games early in the season because of the injury, which cost him a place in the USA squad for the final link-up before the World Cup. He was then left out of the World Cup squad two months later, an omission which he admitted left him "shocked, mad and heartbroken".

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The 28-year-old was an ever-present for Boro in the second half of the season, with Michael Carrick telling of how the goalkeeper was a "big part" of his side's success.

With Boro's season ending a couple of weeks ago, Steffen headed for Barcelona for surgery, with reports in USA saying the procedure was to clean out meniscus damage.

Steffen posted on his Instagram: "In life there are times when you have to take a step backward in order to progress further, stronger and wiser.

"God has a plan different from our own.

"I'm grateful for all who have helped me these past couple of weeks. I'll be back soon."

Sol Brynn signed a new two-year contract at the Riverside earlier this week on the back of his impressive Swindon Town loan, but Boro will still look to bring in a keeper this summer. Steffen's substantial Manchester City wage means a permanent move to Boro is extremely unlikely. With two years left on his City contract, it's not clear if the Premier League champions would sanction another loan move for next season.