Ibrahimovic had a fine debut year for United, netting 28 goals in 46 appearances in all competitions during the 2016/17 season as Jose Mourinho's side went on to win the Capital One Cup and Europa League.
The former PSG striker did, however, miss the end of the season after suffering a serious knee injury in a Europa League quarter-final clash with the Red Devils deciding to release him following the expiry of his contract.
Saha, who played for United from 2004 to 2008, believes the 35-year-old will prove to be great competition for Romelu Lukaku and can galvanise the entire team.
"Ibrahimovic is an immense player who will galvanise the squad during the second half of the season," Saha told Omnisport, as quoted on FourFourTwo. "Competition for places within the squad is great."
"Leadership is vital to win trophies like the Premier League and Champions League. I cannot wait for him to resume playing again at Old Trafford."
As for Lukaku, Saha said the Belgian international, who has already impressed many with his start for United, could be as crucial as David De Gea when it comes to challenging for the top honours.
"Lukaku is the player who can score 25 goals a season but he is also capable of scoring the very decisive ones," Saha added.
"He is a very important element, as much as [David] De Gea and the quality of the bench to win a title."
Mourinho's men will hope to improve on their 100% record so far as the table-toppers travel to Stoke City next on Saturday (9 September).