Seaman expects Arsenal boss Wenger to buy this summer
Seaman said it was obvious where Wenger needed to strengthen.
"He has got to sign a central defender - and someone who is the finished article, an established centre-half, rather than a developing player," he told the London Evening Standard.
"This season they've had a number of injuries to key players (including Fabregas and Robin van Persie) and that cost them.
"Even then, they still had chance to win the league with three games to go and that was more than was expected of them at the start of the season."