But the newspaper adds that West Brom remain hopeful of concluding a loan-to-buy deal before Friday's 5pm deadline, and are likely to return with an improved bid.
Dack has enjoyed an impressive start to life in the Championship, scoring two goals in his first three appearances at that level.
The newspaper claims Tony Mowbray, the Rovers manager, is a long-term admirer of Vela, who is thought to be valued around the £5 million mark despite having entered the final year of his contract.
And that sort of offer could be tempting to Bolton, despite the Trotters' reluctance to sell key players before the window closes.
Dack, who moved to Blackburn in a £750,000 deal from Gillingham a year ago, could replace Nacer Chadli, the wantaway West Brom player, at the Hawthorns.
Would Blackburn's Dack and Bolton's Vela be good additions for West Brom and Rovers respectively?
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