The former Gunners is expecting Arsene Wenger to make more signings.
The Gunners were expected to spend big this summer to bounce back from the disappointment of last season.
That has not proven to be the case though, with Granit Xhaka the only major arrival at the Emirates so far.
Arsenal's Granit Xhaka
That has seen Arsene Wenger coming in for criticism about spending once again, especially with both Manchester clubs spending big money to improve their squads this summer.
Hartson, though, says he believes the Frenchman will surprise everyone with a couple more signings before the window closes.
“They need another centre-half and a striker,” he told BBC Sport.
“But I picked Arsenal to finish second because I think they will add another couple of players before the window closes – I think Wenger may surprise us there.”
Arsenal manager Arsene Wenger
It remains to be seen if any more signings do arrive at the Emirates before the transfer window slams shut.
A central defender looks extremely likely to arrive given the fact that the injuries to Per Mertesacker and Gabriel Paulista have left them seriously short in the position.
Another striker should be on their shortlist too, but all indications appear to be that one will not be arriving. Gunners fans will be hoping that doesn’t prove to be the case and Hartson’s prediction comes true.
Arsenal manager Arsene Wenger before the match