Martin Keown believes England defender John Terry could struggle for form at Euro 2012, as the Chelsea captain continues his recovery from a hamstring injury.
Terry missed full training with England on Tuesday but remains on course to be available for England's Group D opener against France on Monday.
The former England captain complained of a tight hamstring in the wake of Saturday's 1-0 victory against Belgium but a scan on Sunday revealed no serious damage and manager Roy Hodgson remains optimistic that Terry will resume full training later this week.
England's defensive injury problems in the build-up to the tournament ensures Terry's fitness remains a key consideration for Hodgson but Keown believes the defender's form should be of greater concern.
"John Terry's form... concerns me. He has played just 70 minutes since the last day of the season and had a very poor game at Liverpool a week before that," Keown told the Daily Mail .
"Terry has said he wished tournaments started straight after the season because that is when he is sharpest. He feels the time off leads to him losing his sharpness and that will very much be the case now. That means he will have to be very strong mentally. Luckily, that is one of his greatest assets.
"Terry's last game in a tournament for England was the 4-1 defeat by Germany at the 2010 World Cup, so he'll just want to get through this without being embarrassed."
Terry's availability has come under sustained scrutiny after Hodgson's decision to controversially select him ahead of Rio Ferdinand, the Manchester United defender.
But Keown insists England have sufficient quality in reserve should Terry's fitness become a problem.
"If Terry's hamstring injury keeps him out at any point, I wouldn't be too concerned," said Keown. "Phil Jagielka and Joleon Lescott each played 90 minutes in the 1-0 win over Spain in November and are more than capable.
"There's very little technically between Jagielka and Terry but the Chelsea captain's experience is the reason he will surely start against France.
"With Gary Cahill injured, Terry will probably play on the right of the central defensive pairing alongside Lescott, as the Manchester City man is left-footed. Usually Terry plays on the left, because he has been more comfortable on that side than whoever he partners.
He added: "That should not be a problem in possession but defensively he will have to make some adjustments, as he will no longer be next to his Chelsea colleague Ashley Cole. I played on the right alongside Tony Adams and Sol Campbell but at Everton I played on the left next to Dave Watson. If you're adaptable it is not a problem and it won't be for Terry."