Those at Emirates Stadium and Old Trafford are in need of reinforcements.
The Red Devils are expected to spend big addressing their apparent flaws, but the same approach is unlikely to be taken by the Gunners.
Unai Emery is reportedly set to be handed a budget of just £45 million ($57m) in which to strengthen a squad that finished outside the Premier League’s top four in 2018-19 and without a trophy.
Arsenal legend Seaman is disappointed to see owners that are hardly short on funds refusing to back their manager in a competitive market that will see a number of rivals splash the cash.
He told talkSPORT: “It’s so frustrating at Arsenal because the club is running on a good profit.
“They’re struggling. It’s just so frustrating being an Arsenal fan and an ex-Arsenal player at the moment.
“You know what the club is capable of, so you’re just like, ‘come on, let’s see what you’ve got!’
“When you look at Manchester United and Arsenal, they’re in a very similar situation – they both need to strengthen at the back and they’re both without Champions League football, so it’s going to be testing times.
“But I’d say United are in a better place than Arsenal because of their buying power and the money they will pay for players.”
While Arsenal may not be as busy as their supporters had hoped this summer, they are being linked with moves for several players – such as Bournemouth forward Ryan Fraser and Belgium international Yannick Carrasco.
Changes are also being made behind the scenes in north London in an effort to make the Gunners more competitive and better placed to challenge for major honours in the future.