The News understands Danny Cowley has been trailing the St Mirren man this summer, as he reshapes his Blues squad.
The likes of Oxford United, MK Dons, QPR and Italian side Sassuolo have been linked with the 21-year-old, who is valued in the region of £200,000.
Erhahon is a player who Pompey have highlighted, with Cowley and his recruitment team carefully following his progress.
They have been impressed with the Glaswegian and see potential in the former Barnsley loanee.
However, it’s been decided Erhahon doesn’t fit the profile of the type of player Pompey are looking to recruit in the middle of the park over the coming weeks.
The promising talent who’s already made 98 senior appearances for St Mirren is viewed as an athletic box-to-box operator.
Cowley, however, is looking for a player with more natural tendencies to anchor his midfield and promote his side’s play from that area of the pitch.
Unlike other areas of the pitch, Pompey’s midfield does not require major surgery this summer.
Ryan Tunnicliffe, Joe Morrell, Louis Thompson and Jay Mingi are the contracted quartet in that department at present.
Cowley has indicated he will assess Mingi in pre-season before deciding if the ex-Charlton and West Ham man will go out on loan next term, with a string of National League and League Two sides keen on services.
Whatever happens there, the Pompey boss would like one more player in that department next term.
He’s already been linked with a number of midfielders including Oxford United’s Alex Gorrin, Preston’s Tom Bayliss and Leicester City’s out-of-contract talent Callum Wright.
Denmead’s Matt Butcher is another midfielder who’s been touted for a Fratton arrival, although The News understands that’s not a move Pompey are looking to advance at present.
Pompey are well stocked in midfield but other areas will require significant focus in the coming weeks, however, none more than the attacking department where the Blues currently don’t have an experienced player contracted next term.
The Blues have been linked with a stack of attacking players as a result, with the likes of Kion Etete and Kyle Wootton on Cowley’s shopping list.
The transfer window opens on June 10, which is when the registration period begins for new contracts. Existing deals for players who are out of contract run until June 31.