If the Gunners parted with the necessary funds to land Lukaku and a new centre-back, Souness has said that it would be enough for Arsene Wenger's men to return to the summit of English football.
"Arsenal are still only two finished articles away from winning the league, provided they're prepared to spend the money required to get them and they're available," the former Liverpool midfielder wrote in his Sunday Times column.
"They need a centre-back to replace Per Mertesacker and a goalscorer - Romelu Lukaku is worth considering. If they need to spend £100m to get them, they should."
Lukaku has scored a total of 61 goals from his 121 appearances in an Everton shirt.