Former team-mate Graham Napier believes Alastair Cook will go down among the true greats of English cricket and perhaps the greatest of all their batsmen after the former national captain announced his retirement from Test cricket.

At the age of 33 and after scoring 12,254 runs, including 32 centuries, in 160 Tests for England, Cook has announced that this week's final game of the five-match series against India will be his last in Test cricket.

The fifth Test of the series, in which England have an unassailable 3-1 lead, starts on Friday at The Oval and it is set to be a poignant occasion for Cook, who captained the national side in a record 59 Tests during his stellar career.

Napier came up as a young player in county cricket and played alongside Cook for Essex and believes, with his former team-mate sitting sixth on the all-time list of Test run-scorers, with a record 11,627 runs coming as an opener, he can be justifiably considered as one of the greats, if not the greatest, of English batsmen.

Napier, who was a pupil at the Gilberd School in Colchester and played club cricket for Colchester and East Essex, said: "Alastair is such a great individual and I believe he'll go down as probably the greatest English batsman ever.

"The statistics don't lie.

"He is the leading England Test runs scorer so he surely must be up there as the greatest the country has produced, certainly the top opening batsman.

"His character is faultless and that's why he's been at the top for so long - he is solid as a rock.

"As a cricketer, I'd say he's been the perfect role model for young players.

"His temperament and approach to the game is amazing.

"He is so level-headed and his overall demeanour means there are no highs or lows and that's critical to a long career at the top that Alastair has had."

Napier, who is 38, had to make his own call on retirement two years ago when injuries finally saw the big-hitting all-rounder step down from Essex duties and he said Cook will have known in his own mind when the time was right to call it a day.

"It's always down to the individual about the timing of a retirement, but if you know when your time is up then that's got to be the time to go," added Napier.

"I think Alastair has had such a great career for England that if he felt he was not contributing runs in the way that he would have wanted then that must have been a factor.

"For me, it was a physical thing as I was struggling to keep playing and when that is the case, it's easy to know when your time is up, but I'm sure Alastair could have carried on for England if he had wanted to as he can carry on batting.

"However, knowing him as I do, if he wasn't performing for the team as he would want, and he hasn't been contributing as many runs for the team in recent games, then he'd feel he was doing the right thing by stepping down."

However, Napier hopes his England bow doesn't mean the end of Cook's cricketing career and said if his former team-mate decides to continue at county level next year, then it would be a huge boost for the club.

Napier, who is about to start his third year in a coaching role at the Royal Hospital School at Holbrook, said: "If Alastair wishes to continue playing for Essex then what a bonus that would be for the county.

"To have someone in his position playing for Essex would be wonderful.

"Having the former England captain in the side would not only be a boost for the team but for the club as a whole."